U.S. Census

Census Data and tools 101.

The Census Bureau serves as the leading source of quality data about the nation's people, places and economy.

In addition to the decennial census, Census Bureau collects and releases data many products....
Economic Census — every 5 years...
Census of Governments — every 5 years
American Community Survey — annually

~130 Demographic, Economic and Other Surveys

Economic Indicators
Foreign Trade data

Oh did I mention the data is available through API via the CitySDK? and the cost is FREE