The famous flea market that visitors mean when they want to go to the Puces is the Puces de Saint-Ouen, just north of the Porte de Clignancourt and therefore not technically in Paris at all but in suburban Saint-Ouen. Right now is a great time to go to the Puces [flea markets] because a lot of Parisians have left for the sports d’hiver, since it’s a long school holiday, and the city is unusually empty. Someone I know even went to the Louvre last Monday and said there was no one there– this rarely happens these days even in the depths of winter.
Although the Puces de Saint-Ouen (at right) is (are?) unmistably huge and interesting, much of it isn’t really a flea market but just antique shops and booths full of high-priced, I mean really high-priced, antiques; then the outskirts is taken up by a lot of uninteresting cheap modern things in booths and on groundcloths near the Périphérique, catering to the large desperately poor population of Paris and its suburbs. (For more affordable things there I go to the Vernaison, Biron, and Paul-Bert markets.)
So Parisians will often tell you that the Puces de Vanves (at left), near the southern edge of Paris, is more of the old spirit, and is their favorite flea market. It’s also not very touristy. What I like about it is that it’s not huge, but on a more human scale, along the sidewalks of the 14th arrondissement for a few blocks, and the atmosphere is very pleasant. (As always, watch out for pickpockets. I didn’t see anyone suspicious, though.) It’s full of Parisians wandering around exchanging greetings; there are many, many regulars. The things for sale are mostly affordable and there’s even a place to get coffee and crepes.