U.S. Department of Commerce
http://www.export.gov/marketresearch.html

Foreign Agriculture Service/USDA
http://www.fas.usda.gov

MSU-Center for International Business
http://globaledge.msu.edu/ibrd/ibrd.asp

Stats-USA--some information is fee-based
http://www.stat-usa.gov

U.S. Trade Statistics
http://www.census.gov/foreign-trade
http://tse.export.gov/