Social Explorer provides quick and easy access to modern and historical U.S. census data and demographic information. The web interface lets users create maps and reports to help visually analyze and understand demography and social change throughout history. The site currently includes data from the entire US Census from 1790 to 2010, all annual updates from the American Community Survey to 2008, original Census tract-level estimates for 2006 and 2007, the Religious Congregations and Membership Study from 1980 to 2000, and 2002 Carbon Emissions Data from the Vulcan Project.
The Integrated Public Use Microdata Series (IPUMS) contains U.S. Census and American Community Survey microdata from 1850 to the present. Also has microdata from the Current Population Survey (labor force), nearly 100 international censuses, Time Use surveys, and more.
The Inter-University Consortium for Political and Social Research. Gold standard of curation, cleaning, and description of datasets. Includes government data as well as researcher-created data, including election data, opinion polls, more.