WordNet (r) 3.0 (2006):

flea market
    n 1: an open-air street market for inexpensive or secondhand
         articles

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "flea market":
   auto show, bazaar, boat show, closing-out sale, commercial complex,
   distress sale, emporium, exposition, fair, flea fair, garage sale,
   going-out-of-business sale, inventory-clearance sale, market,
   market overt, marketplace, mart, open market, plaza, rialto,
   rummage sale, sale, shopping center, shopping mall, shopping plaza,
   show, staple, street market, tax sale, trade fair,
   white elephant sale