Place de la Madeleine has the smallest market in Paris. I think it's on Tuesdays. There are also loads of overly-flash food boutiques on the square that are worth going in to drool. And to feel poor.
The very best market in paris, according to my gourmand parisian grandfather, is Grenelle, in the 15th, metro; La Motte Piquet Grenelle. It's awesome, it's under the "metro aerien" (elevated metro) line which makes for a weird setting and has probably got the finest selection of food I have ever witnessed. I've only ever been on Sundays, but it appears to be held on wednesdays as well. Although I can't vouch for the stalls, I imagine they'll be similar.
The very best market in paris, according to my gourmand parisian grandfather, is Grenelle, in the 15th, metro; La Motte Piquet Grenelle. It's awesome, it's under the "metro aerien" (elevated metro) line which makes for a weird setting and has probably got the finest selection of food I have ever witnessed. I've only ever been on Sundays, but it appears to be held on wednesdays as well. Although I can't vouch for the stalls, I imagine they'll be similar.

I'm looking forward to escargot, steak frites, boudin 
