Administrative Office of the US Courts--The AO maintains data on the activity of the lower federal courts. Coverage is generally from 1988-present, but extends further back in some cases. These data are available here in .pdf format.
Bureau of Justice Statistics--The BJS provides a wealth of crime and criminal justice data compiled by the US government and links to available data on other government websites.
Congressional Quarterly Supreme Court Collection--The CQ Supreme Court Collection is part of the CQ Electronic Library in Databases at Emory. It contains a variety of data on the United States Supreme Court regarding opinion activity, decision dynamics, nominations and justice ideology, among other topics.
Court Statistics Project (CSP)--The CSP (hosted by the National Center for State Courts) collects data on the work of state trial and appellate courts. The CSP produces various statistical resources on caseloads of state courts, including breakdowns by categories of cases (e.g. civil cases, felonies). More detailed data files from the CSP are accessible from the NACJD's State Court Statistics Series.
Disaster Center Crime Statistics--Includes crime data (raw totals and crime rates) for all of the U.S. states from 1960-2011.
General Social Survey (GSS)--The GSS measures public opinion in the United States on a wide variety of topics of interest to social scientists. The survey, which began in the early 1970's, provides a (nearly) annual perspective on American attitudes toward government, life, race, religion, and other social issues. The link here is to the GSS homepage within the National Opinion Research Center. Sites where researchers can extract and download specific variables of interest are listed here. The SDA Archive at Berkeley also holds GSS data from 1972 to 2010.
Georgia Bureau of Investigation Crime Statistics--The GBI maintains state and county-level crime data for the state of Georgia from 1980-2011. The data from the Crime Statistics Database and the Criminal Justice Coordinating Council may be of particular interest.
Georgia Department of Corrections--The Georgia DOC maintains prison population reports and data for the state of Georgia from 2000 onwards in .pdf format.
Historical Violence Database--The Historical Violence Database, which is hosted at the Center for Criminal Justice Research 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.
International Crime Victims Surveys--A "victimization" survey performed in sweeps from 1989-2005, with data from the most recent sweep available and external links to prior surveys. The surveys are also accessible via the NACJD.
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.
National Consortium on Violence Research (NCOVR)--The NCOVR is a multi-disciplinary group devoted to the study of inter-personal violence. The NCOVR's resources include a data center that that provides a web interface to data from the Uniform Crime Reports, the National Incident-Based Reporting System, the National Crime Victimization Survey, and other data collections.
Office of Juvenile Justice and Delinquency Prevention --The OJJDP offers both its database of National Juvenile Justice Data Sets and Data Analysis Tools with particular focus on juvenile activity in the justice system.
Roper Center for Public Opinion Research--The Roper Center is one of premier polling-data archives in the country. Its holdings cover a wide range of topics. The iPOLL search page may be of particular use because it allows users to search at the question level. Roper is also accessible via Databases at Emory.
Social Science Electronic Data Library (SSEDL)--The Social Science Electronic Data Library is an archive of over 300 datasets covering a variety of topic areas such as Adolescent Pregnancy, Aging, AIDS/STD's, the American Family, Disability in the US, and Maternal Drug Abuse. The archive is well-indexed and allows variable-level searches. Some of the studies are also available on CD's in the Data Center. The SSEDL is also accessible via Databases at Emory..
Sourcebook of Criminal Justice Statistics--The Sourcebook compiles data from more than 100 US criminal justice sources. Available in spreadsheet or .pdf formats.
The S. Sidney Ulmer Project--The Ulmer Project hosted by the University of Kentucky provides access to many political science datasets created by and for judicial scholars. Holdings include the Spaeth US Supreme Court Judicial Database and several datasets pertaining to American federal and state courts. Note that the data are currently being migrated over to the Judicial Research Institute.
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 US. Historical data tables taken from the Statistical Abstract are available here. There is also a CD version of the Statistical Abstract available in the Data Center.
United Nations Surveys on Crime Trends and the Operations of Criminal Justice Systems--The UN makes available the results of seven global surveys on crime and criminal justice since 1970 in various formats. The NACJD also distributes some of these data. Some of the data files are also accessible via this UN site.