Peer reviewed articles are probably the best source for data and statistics. For this I recommend EBSCO (All Databases). Books can also be useful.
For the more intrepid, the sources below provide potentially useful statistics and data sets.
American Factfinder. Provides Population, housing, economic and geographic data from the Census Bureau.
Bureau of Justice Statistics. Provides federal statistics about crime. Has links to FBI Uniform Crime Reports and Sourcebook of Criminal Justice Statistics.
Gallup Analytics. Perform searches, create and export custom tables and charts of Gallup U.S. and global analytics.
Social Explorer. Provides demographic information about the US, with maps.
Statistical Abstract of the United States (Proquest). Federal collection of data on social and economic conditions in the U.S., current year and historical.
Polls:
Poling the Nations: Compilation of more than 14,000 surveys conducted by more than 700 polling organizations in the U.S. and worldwide, from 1986 on.
Roper iPoll: Comprehensive polling from the Roper Center archives, 1935 to present, updated daily.