Pew Research Center, a non-partisan think tank of the Pew Charitable Trust, engaging in frequent national polls across the United States.
Kaiser Family Foundation Polls, national polls addressing health issues and health policy in the U.S.
American National Election Studies researches voting, public opinion, and political participation.
Current Population Survey, sponsored by the U.S. Census Bureau and the U.S. Bureau of Labor Statistics. Survey topics include work, earnings, education, volunteerism, school enrollment, health insurance and child support.
Real Clear Politics pulls together political and election polls sponsored by a variety of news sites with differing biases. Compare results and methodology.