Although little known outside of Europe, the Grande Braderie de Lille (the "Grand Clearance Sale" of Lille) takes place on the weekend of the first Sunday of September in Lille, France. The event dates back to the 12th century and claims to be the largest such event in Europe with over 10,000 sellers and several million attendees. This year the event is scheduled for Saturday, August 31st and Sunday, September 1st.
It's not too late to make plans for this year's market. Lille is located on the Belgian border, about an hour north of Paris on the TGV (high speed train). Lille is actually closer to Brussels than Paris, so there are multiple options in terms of flights to Europe and hotel accomodations. As you can imagine, with over 2 million visitors expected it gets a little crowded and hectic in Lille itself. You may want to consider staying outside of Lille and taking the train in during the market.
Needless to say, anyone who attends the Grande Braderie needs to do a little advance prep work. Below are a few links to help you get started:
*Photo courtesy of Owen Franken for The New York Times