Bureau of Justice Statistics: Statistics on U.S. crime, offenders and the justice system. Also links to other government and international sources, criminal justice data sets and abstracts of data sets.
FBI Uniform Crime Reporting: The UCR Program consists of four data collections: The National Incident-Based Reporting System (NIBRS), the Summary Reporting System (SRS), the Law Enforcement Officers Killed and Assaulted (LEOKA) Program, and the Hate Crime Statistics Program.
USA.gov - Data and Statistics: Statistics from more than 100 agencies of the U.S. government.
National Archive of Criminal Justice Data: Research data available from ICPSR, Bureau of Justice Statistics, and National Institute of Justice.