
Statistical Abstract of the United States
American Factfinder - access to aggregated Decennial Census data for 1990 and 2000
American Community Survey - annual sample data similar to the Census long form, beginning with 2000
ICPSR - the main social science data archive; most data sets are available for use with SPSS, SAS, or STATA statistical analysis packages
Data Archives - Sue's listing of data archives
Glossary of Social Science Computer and Social Science Data Terms