One of the things I love the most in Paris is Le Marché du Puces. Personally I prefer to arrive the weekend before PV to enjoy the city and this lovely market before Paris gets crowed with the fair. No matter you're looking for "vintage" or forniture or just to forget about bussines is always worth visiting.
A couple of sites you can find more about it:
Marches Aux Puces & Paris Puces
A couple of sites you can find more about it:
Marches Aux Puces & Paris Puces