Paris is a commodity fetisher's dream, and you can buy stuff anywhere. If you're shopping for particular things, though, certain areas of town are better than others.
For example, inexpensive youth-oriented clothes and shoes are concentrated on and around the boulevard St. Michel in the Latin Quarter. Leather jackets, especially during the sales season, can be especially good deals. (Sale season, by the way, is officially—really!—the month of July, when everything is marked down, often drastically, to clear space for the fall lineups; look for the word soldes plastered in giant letters everywhere.) Regarding shoes, however, be forewarned: French shoes are unreasonably expensive, so no matter where you look for shoes they'll no doubt seem more expensive than they should be. Some of the larger stores like Eram have a decent selection at reasonable prices, but if you're looking for something uniquely French, you're going to pay for it.
You want luxury items? Head for the Place Vendôme and the Avenue Montaigne. (Metro Tuileries or Pyramides for Place Vendôme; Franklin-Roosevelt for Avenue Montaigne.) Expensive. Really. Just shopping for clothes and personal items in general? Well, you have to know about the grands magasins, the big department stores in the 9th arrondissement. Galeries Lafayette, at 40 boulevard Haussmann, and Printemps, at 64 boulevard Haussman, will keep you busy for days (both are at metro Havre-Caumartin). These are giant stores, several buildings each, and they're jammed with merchandise and customers. The sidewalks in front of them are crammed with passers-by and with salespeople demonstrating odd or unusual kitchen products, somewhat reminiscent of wht you'd see at a county fair. These are the places for some of the latest fashions at more reasonable prices than you'll find at the designer shops (although they're not cheap).
By the way, did you know that you've never had a cup of hot chocolate? You haven't, unless you've had the hot chocolate "l'Africain" (accompanied by some pastries) at the insanely good Angelina on the first (French) floor of the Galeries Lafayette main building (and make sure to look at the breathtaking dome as well). I don't know how to describe the stuff: it's the most chocolaty liquid I've ever encountered (and I've encountered more than my share…), and it's got a density and a luscious thickness that are impossible to fathom. You can order it by the pitcher, and truth be told, that's not enough. I wish I could figure out how they make this stuff.
There also used to be the marvelous La Samaritaine, at 19, rue Monnaie in the 1st (metro Pont Neuf). La Samaritaine had a rooftop restaurant that was itself alone a trip to the store. It wan't at all expensive, and you got really nice, clear views of pretty much the entire city from here. UPDATE: La Samaritaine has been closed indefinitely since the summer of 2005. Don't know if it's coming back, but I hope it does. Right now the edifice is empty and it looms scarily, right in the middle of the city.
There's also the Bon Marché (and its shockingly slow-to-load website). "Bon Marché" means cheap, which this place isn't. It's at 24 rue de Sèvres, metro Sèvres-Babylone. This place has all your upscale items in one roof, it's way less crowded and frantic than the grands magasins, and if anything just a little more chic. I've seen celebrities here, actually. Once you're in this area, you can head over to two other good shopping districts: Saint Germain/Saint Sulpice, and Rennes (just walk down the little rue Saint Placide to the rue de Vaugirard and the rue de Rennes).
Sale season is officially the month of July, when everything is marked down drastically. Look for the word 'soldes' plastered in giant letters everywhere.My favorite areas are the rue de Rennes and the surrounding streets, and the area around the Place St. Sulpice (where, by the way, one of the grandes dames of French cinema lives, but I won't tell you who or in which building—just keep your eye out). Saint Sulpice is also the church that figures prominently in The Davinci Code, but it's worth seeing anyway (ha!). The marquis de Sade was baptized there, as was the best poet in the world, Charles Baudelaire. There's a strange and unusual Egyptian obelisk in the church. Go inside—really—and you'll be glad you did. There's an Yves Saint-Laurent shop here that's especially amusing because the staff haven't yet been apprised of the fact that no one cares about snooty designer attitude anymore. Go in and they'll sniff at you and prance around, looking like one of those Saturday Night Live parodies of teenagers working at the Gap.
If you're a watch fetishist, there's only one place to buy watches as far as I'm (and hence you're) concerned: La Montre du Marais, a tiny but excellent shop at 20, rue de La Verrerie (in the marais, as the name would indicate, a very short walk from metro Hotel de Ville). The owner, an affable man who talks very fast, is extremely knowledgeable, and when you walk in (after you've scanned the zillion watches in the display window) he will tell you to browse at your leisure but not to hesitate to ask for help, and then he'll completely ignore you. If you ask to see things, however, he'll suddenly be up and running, not only showing you the watch you asked to see, but others like it. He's especially good at sussing people's styles out, and there's a good chance he'll find one you like better than the one you first picked.
Music and books galore inhabit the FNAC (and no one in the world knows what that stands for, by the way, but it is la FNAC, so I'm guessing the first word is Fédération, or something like that—[A Tom's Guide Mystery solved! A reader—actually it took two readers to get this through my head (thanks, Jan)—points out that not only is the first word, in fact, Fédération, but that the whole thing is Fédération Nationale d'Achat des cadres—thanks!]), and there are two principal locations: in the sickening Forum des Halles (metro Les Halles), where you have to go underground on this scary and too long escalator ride which is made even worse by the wan and destitute looks on the faces of the people opposite you coming back up, making you wonder why you ever embarked on this journey in the first place; and at 136 rue de Rennes, not far from the tour Montparnasse (metro Montparnasse-Bienvenue or Saint-Placide). Although the latter store is more attractive and more pleasant to shop in, alas! the former store seems to have a wider selection. They have tons of books on every conceivable subject (and they're especially good on travel, comic books [bandes dessinées], philosophy, literature, and art), and they have a significant selection of books in English. The music section is a dream come true, and the music is laid out by category in a way that actually makes sense, and each department ("électronique," "variétés françaises‚" etc.) has a little info desk where you can inquire about a particular CD or DVD, and the folks who work there know everything and will actually help you. The best English book store in Paris is not the one you think (that is, the one everyone knows about, and hence deserves no mention here). Actually, it's called the Abbey Bookshop, and it's at 29 rue de la Parcheminerie, in the 5th (in the little pedestrian streets off of St. Michel). They have new and used books here in most conceivable subjects, all at reasonable prices. There are a lot of other bookstores, of course. Tom's favorite place to go book-shopping is on the Rue des Ecoles in the 5th arrondissement. Here you'll find a dozen or so small- to medium-sized bookstores, some specializing in a particular range of disciplines and others just a sort of mishmash of stuff. Many of them have second-hand books for those seeking a bargain. Unfortunately for you anglophones out there, these are all pretty much exclusively in French. Finally, if you're a college student, go to Gibert Jeune, at the bottom of St. Michel and also up the hill a little ways, because that's where college students are supposed to go, and they do. It's got books, notebooks, and all sorts of other things you didn't know you needed but which generations of college students have discovered they've been lacking. I won't buy notebooks anyplace else.
If you want to buy wine or other sorts of spirits and you have no idea what you're doing, go to a specialty shop. The big chain is called Nicolas, and they're all over, but you might also want to go to a mom and pop variety. These people know what they're talking about, and won't try to pressure you to make you buy things that are more expensive and out of your league. There are especially nice and helpful ones on the Ile St. Louis, right in the middle of the rue St. Louis en l'Île, and another at 13, rue Buci in the 6th, both of which are in areas you might find yourself walking around in anyway.
Now this is only for some of you, but if you're of those who believe that chocolate is a near sacred substance that should be prized as much as platinum—that is, if you have an ounce of sense in your head—then run over right now to Debauve et Gallais at 30, Rue des Saints-Pères in the 7th arrondissement (but almost the 6th: 01 45 48 54 67, metro Saint-Germain des Prés or Sèvres-Babylone). You will swoon as you enter the storefront (which is classified as a historical monument), and you will become drunk with chocolate lust as you contemplate the displays laid out before you. This establishment has been around since 1800, when Sulpice Debauve, who had been pharmacist to Louis XVI (guess that didn't work out so well) not far from the current location. You can buy a ton or a single piece. I once asked them for the richest piece they had and they gave me a bite-sized piece that was so dense I actually couldn't finish it.
Grocery stores aren't anywhere near as big or as numerous as they are in the U.S. Look for Inno, Franprix, or Monoprix, chains of supermarchés (but the really big ones are called hypermarchés, which makes me conjure up a very amusing image). Most of these stores are somewhat cramped and impersonal, and the change crisis continues even after the adoption of the euro. You'll have to bag your own groceries, but you'll find whatever you want here (including spirits). If you're a food snob and you want really fine foods, check out either Hédiard or Fauchon, both on the Place Madeleine (metro Madeleine). You'll find all sorts of wild things here (including peanut butter!), and the staff is attentive and knowledgeable. (I once worked at the Hédiard in the sixteenth arrondissement [70 avenue Paul Doumer, metro Passy or La Muette], and I was very attentive and knowledgeable. You'll want to drop by to see where I worked as a lad). If you want to get someone an interesting food gift, try the pâtes de fruit at Hédiard: they're a more sophisticated version of those jelly candies coated with coarse sugar you got in the movie theaters when you were a kid, but these come in a variety of adult flavors, including bitter orange and blackberry, and you can have them packed in attractive gift boxes. They're strangely addictive.
BTW, if you want something gift-wrapped, you tell the salesperson that it's "pour offrir" (literally, "to offer").
Like to shop around for junk, in search of that amazing find—whether a Persian rug, a Renaissance-era dining table, or a vintage 1950's ashtray? Then you have to see the marché aux puces de Saint-Ouen. A marché aux puces is a flea market, and this one's absolutely huge, with an absolutely enormous variety of stuff. Take the metro out to Porte de Clignancourt and follow the crowd down the street. Then browse something live 2000 different booths, some indoor, some outside. The market is open Saturday, Sunday and Monday, from early morning until late afternoon-early evening. This thing has been around for over 100 years, and you might be put off at first by the throngs of people there, but it's worth it to see all this stuff. (Do watch your wallet or bag, though; this place has some operators.) There are also some pretty decent restaurants and cafés in the area surrounding the market (mostly to the north and east), so you can even make a day of it—but only on Saturday, Sunday, and Monday, from 10:30 until 6:00.
Les bouqinistes are booksellers who have these green stalls built in along the walls looking over the Seine. Generally speaking they have a lot of old books and magazines, and you're unlikely to come across any rare first editions or anything (these people aren't idiots—they know what they're selling), but you might find the odd interesting old print or whatever. The thing about the bouquinistes is that even if you don't find anything interesting to buy, it's really fun to shop here.
A lot of people are intimidated about looking at or—gasp!!—trying on clothes in Parisian boutiques. Well, don't be. Well, wait—be, but learn how not to be. Although this is less the case than it used to be, a lot of salespeople in clothing stores (and I'm not really talking about the big department stores here) can still be a little high pressure. So what? There's a little drama that might play out, and as long as you play the role you're supposed to play, instead of the one a pushy salesperson might want you to play, you're fine. They'll want you to feel bad for trying something on and not buying it. If some wise acre tries to pull this on you, you trump them by acting offended that he or she would even think of selling you something of such inferior quality, and that you're lucky to have noticed, at just the last minute the defects the merchandise sports. Always maintain the moral high ground if someone tries to pull this crap on you (although it's unlikely). The bottom line here: don't be afraid to try things on even in the smallest, trendiest boutique. Just be armed (and now you are) with all the cultural weaponry required.
Speaking of buying clothes, there used to be—and as far as I can tell it's gone—at least one vending machine for buying... blue jeans. It was the weirdest thing I ever saw, and it was this big sucker right in the middle of the giant Auber RER station. It was bigger than a photomaton (those booths you can get your picture taken in), and you'd stand inside it, pull this sort of cord thing around your waist to determine your size, insert your credit card, and out would come a pair of blue jeans. I couldn't ever figure this out: was this in case you accidentally left the house without wearing any pants?