Paris Museums
I started adding museums on to the page on Tourist Stuff, but it was getting too long, hence this separate page. These are some of my favorite museums in Paris, and I've listed below some of the ones you may not think of or hear much about.
You're going to the Louvre, of course. That's not an assumption, it's an order.
You're going to the Louvre, of course (metro Palais-Royal or Louvre). That's not just an assumption, it's an order. Six million other people will be going this year, so you don't want to be left out. Even if it's only to see the Mona Lisa (La 
Joconde, as she is known to Pierre and Mireille), you go to the Louvre and you'll be stunned. The way to do the Louvre is to avoid the cattle-like crowds who shuffle along as though marching dutifully to their deaths. So, don't follow the signs cheerfully directing you to Mona (we're on a first-name basis). That's what's happening in the image to the left, and it's decidedly unpleasant when the place is crowded (consider going at odd hours, by the way). Instead, enter the museum through one of the less-popular exhibits. 
Note that there are several entrances to the Louvre, not just the main one inside the pyramid (although I have to admit I love going down the inside of the pyramid). Those other entrances will be far less crowded, and they are at the Place de la Concorde, the rue de Rivoli, the Quai des Tuileries, the avenue du Général Lemonnier, and the Passerelle Solférino. Thing is, they're more or less randomly closed, and the Louvre is huge, so you might end up walking around the thing a lot. But at least you won't have to wait in line. (Go here for an illustration of the secret entrances.) It costs 9 euros 50 to get in, but you can go for free on the first Sunday of each month (and everyone else has the same idea, so be forewarned). The Louvre is closed on Tuesday. The trick with the Louvre is to go to the areas in which people are not going. You'll find all sorts of interesting things, and you'll end up working your way around to the "must sees" anyway, so, as usual, just do what I say (the people to the right are engaged in an activity that mystifies me: they're taking pictures of the Mona Lisa, and they'll kill each other to get a good spot, so I took pictures of them). I like the underground parts that show you the history of the structure; the Greek pottery; and the room that has a sixteenth-century portrait of an Italian gentleman who looks like, well, me. Consider having lunch at La Frégate, which is sort of across the street, where the Quai Anatole France meets the Quai Voltaire.
OK, that one was a given: everyone has to go to the Louvre. But here are a couple of places you might not think of that are either off the beaten path (I hate that expression) or interesting, or weird, or scary, or something I can't identify.
The first one is one you probably know about, and it's not really off any path, beaten or otherwise, but I felt like mentioning it because I like it and because I took these photos there that I like. It's the Musée d'Orsay, and it's pretty remarkable (metro Assemblée Nationale, Solférino, or Concorde in a pinch). Like most state museums, this one's closed on Tuesday and free the first Sunday of the month. Otherwise it's 8 euros to get in. (Read the back of your ticket. The part in English says something like "Closing time 4:00. Or 6:00." I love that.) The most popular part of the Musée d'Orsay is probably the section dedicated to impressionism (yes, they have "Starry Night"), but you should also check out the salle des fêtes—the museum is a former train station, you realize (see the clocks?), and the salle was—and still is—an incredibly ornate reception hall. This is on the second floor, and it's remarkably fussy and elegant and cool, and it's got a number of interesting bits of art in it as well. You an even rent this space out for your own events (you'll want to book early, and start saving up now). Don't miss going up to the very top of the museum, where there's a restaurant and a snack bar. If it's nice out, you can go out on the terrace and get a simply stunning view of the city. You can also stand behind the giant clock that faces outwards onto the street from the station, and kiss a complete stranger (as at above right, although I suspect these two already knew each other).
You say you like impressionism? and especially Monet? Then you should lay tracks over to 2 rue Louis Boilly in the 16th to the Musée Marmottan (metro La Muette). This museum has the largest holdings of Monet in the world, and it also contains significant works by the other major French impressionists. This isn't a state museum, so it's open every day. It's worth a visit just to check out the beautiful surroundings, since it's located very near to the Bois de Boulogne. The building is also worth a visit in and of itself.
You might not expect it to be as fabulous as it is, but the Musée Rodin will calm you and excite you at the same time. It's at 79, rue de Varenne, and you can reach it via metro Varenne (or Invalides in a pinch). It's open every day except Monday, and admission is 7 euros (free first Sunday of the month). Entrance to the exceptionally cool garden only—that is, no museum visit—is 1 euro. One of the things that makes this museum so appealing is in fact the lovely garden, complete with its amazing Rodin statues. The house is majestic and stately, and you haven't seen a work of sculpture until you've seen Rodin's rotund Balzac. You got your Gates of Hell, and oh, yeah, there's that Thinker guy, too.
The Musée National des Arts et Traditions Populairs et Centre d'Ethnologie Française is now closed (and thanks to Chani for pointing this out to me). The museum was way the heck out in the 16th arrondissement at 6, avenue du Mahatma-Gandhi, and the following description will tell you what you're missing until the collection is relocated to Marseille: The closest metro is Les Sablons—exit the metro and head south on the rue d'Orléans, and hang a right on the avenue du Mahatma-Gandhi. It's a bit of a hike, but if it's nice out, you're right near the Bois de Boulogne (actually, you're kind of in it), so that can be part of your trip. The museum itself is strange and odd, but weirdly appealing. They have all these exhibits and dioramas that are supposed to represent life in France from the year 1000 forward, and it takes a while to catch on, but once you get into it the whole thing becomes weirdly compelling. You're walking around in these darkened rooms and it's all very theatrical and cool. Kids will probably especially like this, since you get to see how the "peasants" lived and what a blacksmith did and whatnot. Lots of crafts and things. I can't remember how much it costs to get in, and that web site is so crappy that they still list the cost of admission in francs! FWIW, it was 22 francs back in the day (3 or so euros, but that's certainly changed by now). Maybe someone can go and tell them to fix their web site.
Admit you were wrong, eat some crow, and go to this museum.As I mentioned elsewhere, one of my very favorite museums in Paris is the Musée Carnavalet, which bills itself as "the most Parisian of all the capital's museums." That's because this is the museum of the history of Paris, and before you make any cracks about how dry that sounds, just wait a second and think about all the really cool things that might be in there. Like a letter that Robespierre was writing when he was arrested, like all these really amazing colorful wooden signs designating commercial establishments that date back to the sixteenth century when folks couldn't read and had to rely on pictures, like the big grotesque heads that used to adorn the Pont Neuf, like all kinds of stuff, so just admit you were wrong, eat some crow, and go to this museum. It's at 23 rue de Sévigné in the lovely Marais (metro Saint-Paul or Chemin Vert). If it happens to be the 13th of July, you can hang out here and go to the bal des pompiers (fireman's ball) later. Situated in a fantastic, elegant, and very large private mansion that Mme de Sévigné once inhabited, this museum is also an architectural curiosity. It's free of charge to visit the permanent collections. Go on a Sunday afternoon, and then walk around the Marais afterwards. Eat falafel.
While you're in the Marais, make absolutely certain to go to the Musée Picasso. [THE PICASSO MUSEUM IS CLOSED FOR RENOVATIONS UNTIL—PROJECTED— SUMMER 2013.] Situated in the Hotel Salé (yep, that's it at right), at 5 rue de Thorigny in the 3rd arrondissement, the museum is open every day except Tuesday, and the price of admission is 8 euros 50. (Closest metros are Saint-Sebastien-Froissart, Chemin Vert, or Saint-Paul.) The museum is situated in this fantastic elaborate seventeenth-century mansion, and it contains something like 3000 works by Picasso, in all the media he worked in. It also houses his own collection of other artists' works (including works by Cézanne, de Chirico, and Dégas). The museum is especially well designed, and if you're someone who gets easily museumed out (you know, that stunned stupor you can sometimes find yourself falling into from looking at too many works of art for too long), you'll find that the arrangement of the works and the layout of the exhibition somehow keeps everything looking fresh. Even if you're not a museum person you'll very likely like this one. I find it one of the most compelling museums in Paris (next to Carnavalet, of course).
Surprisingly more interesting than you'd expect is the Musée des Arts Décoratifs, which also houses exhibitions on fashion and textiles, as well as on advertising. Located behind a very forbidding looking wall at 107 rue de Rivoli (metro Palais-Royal Musée du Louvre or Tuileries), the museum is open Tuesday through Saturday and it costs 9 euros to get in. This thing has examples of pretty much anything anyone ever put in a cave, hut, house, mansion, or hovel to decorate the place and call it home. There's also an exhibit of advertising posters and paraphernalia that's quite captivating, and even if you don't care a whit for the fashion world or clothes you'll find these exhibits—if only in small doses—oddly attention grabbing.
Weirdly, even tough I lived within a stone's throw for a while, I've never been to the Musée Grévin—a wax museum—which is at 10, boulevard Montmartre in the 9th (metro Grands Boulevards). Someone go here and report back, OK?
Perhaps in the same general category as the Musée Grévin is the Musée de la Magie, at 11 rue Saint-Paul in the 4th arrondissement (01 42 72 13 26, open Wednesday, Saturday, and Sunday, from 2:00 to 7:00 pm). This place insists that France has the richest history of magic in the world, and judging from all the things they have here—from big illusions (such as the woman sawed in half), to optical tricks, to posters and engravings from all over the place—they might be right. There's also a school of magic, with a syllabus that includes things such as cards, ropes, and everyday objects, as well as a magic store. Get all your magic needs here.
Perhaps the coolest thing—and it's pretty cool—about the Musée de Montmartre is that it's right next to the last operating vineyard in Paris. Really. If you don't believe me that there is such a thing, look here, where I told you about the Fête des vendanges de Montmartre. Now do you believe me? This museum is located at 12, rue Cortot in the 18th (of course) and your closest metro is probably Abbesses (which ain't all that close, really, but you'll have a lovely stroll. If you're not in great shape, take the Funiculaire up the hill). At 8 euros a pop, they'll let you in any day except Monday and Tuesday, and the collection holds some terrific stuff on historic Montmartre and the artists who made it famous (again) in the nineteenth and twentieth centuries. This place is somewhat small, but if you're interested in Montmartre, you'll find the collections here quite absorbing. If you're just so-so on Montmartre, you can pass this one up.
The Pompidou Center is officially known as the Musée National d'Art Moderne Centre Georges-Pompidou, but it's also often referred to simply as Beaubourg (and their web site is especially good—check it out). When the Center opened in 1977 it was all the rage and the hot controversy was that it had all of its guts (heating, exhaust systems, plumping, etc.) on the outside (see left). It seems much less controversial and avant garde now, but that shouldn't stop you from visiting this marvelous place. The Pompidou Center is the national museum of modern art (as the name implies), and the collection is housed on the 4th and 5th floors. Taking the escalator up is part of the fun, because the escalator is in a glass tube on the side of the building, and as you rise up above the rooftops you get a simply splendid view first of the Center's neighborhood, and then of the entire city. The view up to Montmartre and Sacré Cœur is especially good. The collection is quite fine, actually, and there are so many featured exhibitions that you can go here very often and see something new each time. There's also a fabulous library here, materials for sharpening your foreign language skills, and IRCAM, the Institut de Recherche et Coordination Acoustique/Musique. You'll also get a major kick out of the street performers who do their shows in the great and vast plaza in the front of the museum—you'll find anything from mimes to Tuvan throat singers here (and this place is especially active on Sunday afternoons). The Center is at 19, rue Beaubourg, and the metro is Rambuteau (Châtelet or Hôtel de Ville in a pinch), and it's open every day except Tuesday. 12 euros.
The oldest buildings in Paris—they're actually Roman baths—are part of the Musée de Cluny which you'll walk by a dozen times in the Latin Quarter before it occurs to you, if it ever does, to go in. This would be your national museum of the middle ages (and don't you just love that someone has a national museum for that?), and I promise you'll find it oddly compelling. Heck, just looking at the cats through the iron grating that faces the boulevard St. Michel is fun, but go around back to the entrance at 6 place Paul Painlevé, pony up your 8 euros (but don't go on Tuesday), and check out the stunning collection of gothic sculpture, medieval jewelry, and tapistries. The main building is a late fifteenth-century building, built to house the Cluny monks, and one of my favorite things here are a few of the giant heads that were decapitated from figures adorning the western facade of Notre Dame. During the French Revolution, the 28 kings of Judea all lined up above the three entrances at the front of the cathedral were thought to be the kings of France, and in the spirit of revolution, the crowds beheaded them. It wasn't until 1977 that the heads were unearthed (and I want to say they were found in the 9th arrondissement, but I'm not sure about that), and you'll be surprised to see how huge they are.
Not really a museum, the crypt of Notre Dame is something you should check out anyway.If you are as obsessed with Notre Dame as I am, you'll like—but perhaps not love—the Musée Notre Dame. This museum, which admittedly isn't for everybody, is at 10 rue du Cloître Notre Dame (just around the left side of the cathedral as you face it), and it has information about the history of the cathedral, the organ, and other things related to the middle ages and the construction of the edifice. It's only open at odd times and on strange days—something like Sunday, Wednesday, and Saturday—and you could easily be alone in the place. I find it weirdly charming and boring at the same time, but, again, I'm wildly interested in the history of Notre Dame. (And here's something I bet you didn't know about the cathedral: a portion of the Crown of Thorns is displayed the first Friday of every month, but you have to know when—and if you ask nice, I might tell you. It no longer has any thorns, though.) Not really a museum, but something you should check out anyway is the crypt of Notre Dame. If you look at the ground in the huge square in front of the cathedral you'll see these outlines in brass. Those indicate the placement of medieval buildings that were once situated here that were torn down to provide a panoramic view of the cathedral. Underneath this giant plaza is a dig dating back to pre-Roman times. The entrance is at the far end of the square, and you have to look for it. Do it—the creepy, ancient space will freak you out and fascinate you as you realize people lived and walked around and ate and slept here a long, long time ago.
Dedicated to the art and culture of Arab and Islamic civilizations, the Institut du Monde Arabe is simultaneously museum, library, and médiathèque. Its further mission is to enhance understanding of 
cultural and scientific exchange between France and the Arab world. A relative newcomer to the Paris museum scene—it was opened in 1987—it presents you with stunning architecture right from the get-go. The building's southern facade is composed of hundreds of ornate diaphragms resembling the iris of your eye that adjust the size of their openings depending on how much light strikes them. These are called moucharabiehs, and they adorn many windows in classical Arab architecture; their goal was to permit people inside the building—presumably women—to look out without being seen. The northern facade of the building follows the curve of the Seine and opens out toward the Jussieu campus of the University of Paris. You'll find the Institute at 1, rue des Fossés Saint Bernard in the 5th arrondissement (metro Sully Morland, Maubert-Mutualité, or Jussieu). There's a fabulous café on the roof. It's closed on Monday.
Worth more than just a quick look, the Musée National des Arts et Métiers is over by République, at 60 rue Réaumur (metro Arts et Metiers or République). Closed on Monday. This museum houses 100,000 objects and drawings concerning inventions in industry, photography, technology—especially textiles, and science in general.
Readers' Suggestions
David B. has this to say about the museum pass: "I debated long and hard about purchasing a Paris Museum Pass but decided to go ahead and do it. It did help us skip the lines at the Louvre and the Musée D'Orsay so I would say it was worth it but the longest line we were in was at the Sainte Chapelle. That was a security line that everyone has to go through, pass or not. The same with the Notre Dame Towers. So people should be forewarned of those downsides to the pass."