Markets/Shopping in Paris

Do you mean next year? Rick's Paris book lists a number of markets which are open various days of the week. I'd start there.

The flea markets are open on weekends; I can't think of one that is open during the week. Daily markets during the week are mostly food with some cheap clothes and household goods. They are kind of pointless if you aren't shopping to cook at an apartment.

My favorite flea is Vanves at that Metro stop. It is on the weekend mornings.

The Marche d'Aligre is in the 12th...open Tues - Sunday. Not only do they have the typical fruit - veg - cheese, etc. stalls, there is also a small flea/antique market that is there every day in the Place d'Aligre, attached to the marche. It isn't huge but there is quite a lot of random, great stuff for sale. Closest tube station is Ledru-Rollin.
Unfortunately, it's only open Saturday, Sunday, and Monday, but my favorite flea/antique market is the one up in Clingancourt...it is massively huge - you can easily spend an entire day or more to see it all. If you just want to spend a few hours you can see a bit of it. It's contained along several streets to the north of the metro station and to the west of the Avenue Michelet that runs directly north form the metro station. As you walk straight north on the Avenue Michelet from the metro station, and you start to see vendors selling athletic shoes, sports jerseys, etc., turn left up Rue de Rossiers and you'll be in the thick of it. Buildings and shops both large and small, everything from absolute junk to stuff pulled out of chateaux. It's a fantastic place to browse! When you first get off the metro, the area seems a little rough but just keep walking and you'll be there. AMAZING stuff.

Many areas have street markets open once or twice a week. The market on Blvd. Richard Lenoir near Place de la Bastille may be the most famous, open Thursday and Sunday mornings only.