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.
Collection of data measures spanning all U.S. states, counties, cities, metropolitan areas, and zip codes. Data goes back more than 20 years. Covers the economy, education, crime, government finance, health, population, religion, social welfare, and transportation.