The Census Bureau stopped releasing new data in American FactFinder (AFF) at the end of June 2019 and transitioned to data.census.gov for data releases formerly on AFF. AFF will remain as an archive system for data and functionality that are not yet available in data.census.gov until March 31, 2020. After March 31, 2020, our American FactFinder will be decommissioned and no longer available.
The Congressional Research Service provides detailed information to Congress on a wide range of issues, most of them packed with statistics. No web site has all of them, but UNT collects a good number of them.
Stats about American cities: residents (race, income, ancestries, education, employment...), geographical data, state profiles, crime data, cost of living...etc. Careful - this site does not always list the sources of its data.
Data is available on a wide variety of demographic information, in spreadsheet formats, on race, income, housing, building permits, employment, transportation, etc. plus links to labor force, per capita income, population and regional consumer price index information.