Gallup Inc.: world class public opinion polling organization with a focus on politics and economics, but other issues included too
U.S. Census: The Census Bureau provides information on a variety of educational topics, from educational attainment and school enrollment to school costs and financing.
Census data page: Census data.
Pew Research Center: Washington, D.C. think tank that specializes in polling the trends that shape American life--demography, internet use, religion, and the press. Follow the navigation tabs at the top of their homepage to see data sets about internet use, religion, etc.