Data sets are available through ICPSR

The Library's Numeric Data Services

Provides help in downloading and choosing data sets
Roper for public opinion polls
Webstract/DRI-Pro (U.S. and international economic/business data)
Help with Correlates of War using Berkeley program

Statistical Resources on the Web

Is one of the best known web sites
Political Statistics lists print and web sources of poll data

Statistical Universe

identifies print, microform, and web sources