ICPSR (Inter-University Consortium for Political and Social Research) This link opens in a new window
"ICPSR is an international consortium of more than 700 academic institutions and research organizations devoted to providing leadership and training in data access, curation, and methods of analysis for the social science research community. ICPSR maintains a data archive of more than 500,000 files of research in the social sciences. It hosts 16 specialized collections of data in education, aging, criminal justice, substance abuse, terrorism, and other fields" (from the ICPSR About page).
Of particular concern to Political Science, the data include legislative voting records, electoral statistics, and public opinion polls. The data files are configured for analysis through SAS, SPSS, or STATA software, so users must be at least modestly conversant with those applications. Criss Library's student computers include both SPSS 20 and SAS 9.3 packages.