Bureau of Justice Statistics
The BJS provides a wealth of crime and criminal justice data compiled by the U.S. government via a variety of data-collection programs. The BJS also provides various tools to produce and download tables on topics such as crime rates, crime victimization, and corrections populations. Many of the BJS' data collections are available via the National Archive of Criminal Justice Data.
Historical Violence Database
The Historical Violence Database, which is hosted at the Criminal Justice Research Center at Ohio State University, is (to quote the website) "a collaborative research project on the history of violent crime, violent death, and collective violence." Data from the project are available for the United States and other countries.
National Archive of Criminal Justice Data (NACJD)
The NACJD provides online access to and analysis of crime and justice data from federal and state agencies. The data cover topics such as attitudes towards crime, crime stats from official agencies, and the functioning of the criminal justice system.