I finally went to Les Puces de Saint Ouen (the biggest and most well known Flea Market) last week-end. I followed the excellent instructions/map from OhHappyDay which really helped me navigate not only public transportation there, but also getting to the actual Flea Market. Most people think the swap meet is the flea market, but if you see this type of knock off stuff for sale, you are definitely NOT at the flea market.A few words of caution, DO NOT carry your cash or credit cards in a purse or back pocket in this area, and DO NOT head back to the metro from any other street than the one in the OhHappyDay map. There is an entire tent city of homeless people under other parts of the bridge and the people hanging out next to the soccer field are very edgy, druggy, and easily provoked (and this was at noon on a week-end). If you are familiar with how the Bronx or Tijuana used to be, this is the Parisian version, so just stay on the main roads as they said in "An American Werewolf in London"!
You must get to Rue des Rosiers before you are in the center of the actual markets of Saint Ouen, and there is a handy map of the stalls online or on the street once you get there.
There are 15 markets in all and some are marked with huge signs
while others have more discreet ones like these
the stalls may line cobblestone alleys
or be scattered amid two story modern metal structures.
Some of the antiques cost thousands of euros, so there are beautiful displays
where you can peruse the unique furniture
and sparkling chandeliers.
My favorite piece was this transportable wardrobe which likely served a well to do traveler aboard a ship a few decades ago. In perfect condition and at 2900 Euros, it could serve as an armoire in a Parisian apartment today :)