Data.Gov is a central portal for datasets, both statistical and geospatial, that are produced by the Federal Government of the United States. While the site is not exhaustive in its coverage, it does include data from multiple agencies within the federal government. The data catalog is located at http://explore.data.gov/.
Statistical Abstract of the United States
Electronic version of the popular resource. The Statistical Abstract contains a wealth of information on numerous socio-economic and demographic indicators for the U.S. Historical data tables taken from the Statistical Abstract are available here. There is also a CD-ROM version of the Statistical Abstract available in the Data Center, and the tables on the CD-ROM version often cover more years of data/statistics than do the print or on-line versions.