USA Trade Online
This site is a joint project of the Commerce Department's STAT-USA and the Census' Foreign Trade Division. It offers very detailed U.S. merchandise trade data. Specifically, it offers data on the export and import of more than 18,000 commodities via "2- through 10- digit HS detail." The time span ranges from the current month to historical data. This is a fee-based service; currently it costs $300/year or $50/month.
http://www.usatradeonline.gov/