Nonpartisan fact tank that provides information on the issues, attitudes and trends shaping America and the world. Conducts public opinion polling, demographic studies, media content analysis and other empirical social science research.
Archive that preserves data from polls conducted by many leading survey organizations for the use of researchers, students, and journalists. Also has a link that shows how to cite polling data.
Polling, Policy, and Public Opinion by 
Polling and the Public by 
