A "Knight News Challenge-funded project to make it easier for journalists to write stories using information from the U.S. Census bureau. Place profiles and comparison pages provide a friendly interface for navigating data, including visualizations." If you've ever tried using the Census Bureau's American Factfinder, this is heavenly.
Census Bureau's main interface for retrieving demographic data from the American Community Survey, Decennial Census, and their Population Estimates. Can get complicated to use -- see Help to view tutorials.
Census Bureau publications on a wide variety of social and economic characteristics of the population, such as household composition, ethnicity, and income. In-depth reports are prepared on important social, economic, and demographic issues.