Essential Resources for Locating and Using Numeric Data

Harvard Dataverse Network
The Harvard Dataverse includes the world's largest collection of social science research data. Collections include data sets from government entities, universities, and individual researchers. Data can be downloaded in multiple formats, if permissions allow, and in some cases subset for analysis.

Inter-University Consortium for Political and Social Research (ICPSR)
One of the world’s oldest and largest social science data archives; based at the University of Michigan. Categories of datasets include census enumerations; community and urban studies; economic behavior and attitudes; government structures, policies and capabilities; social indicators; and much more. 

Roper Center for Public Opinion
Access to aggregate and raw public opinion data. While the data collection focuses strongly on United States public opinion, it also includes growing collections of (micro-level) European, Latin American (Latin American Databank) and Japanese (JPOLL) polls.

re3data.org
A global registry of research data repositories from different academic disciplines.