Bureau of Justice Statistics (BJS)
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.
Center for Empirical Research in the Law (CERL)
CERL, which is hosted at Washington University's School of Law, "supports the application of sophisticated empirical methodology to legal studies research." Its various projects cover topics such as judicial ideology measures, Supreme Court opinions, and even a legal encyclopedia of popular music.
Judicial Elections Data Initiative (JEDI)
The JEDI ( ... ) project at Washington University's School of Law is devoted to collecting "data on elections to state courts of last resort from 1990 to 2010 in an effort to facilitate replication efforts and to stimulate new research in the area of state judicial selection."
Judicial Research Initiative (JRI)
The Judicial Research Initiative at the University of South Carolina has brought together multiple datasets that are of interest to students of judidical politics, covering topics such as attributes of court cases and justices at various levels of government and measures of judicial ideology. Harold J. Spaeth's data on the Supreme Court may be of particular interest. The Spaeth Supreme Court data also reside at http://supremecourtdatabase.org/
National Archive of Criminal Justice Data (NACJD)
The National Archive of Criminal Justice Data, which is hosted at the ICPSR, is an extensive archive of data about crime and the operations of the criminal justice system. Please note that many NACJD data collections are now restricted and available via application only.