Polling Data (http://www.pollingreport.com/index.html) - PollingReport.com states that it is "an independent, nonpartisan resource on trends in American public opinion." You can find an extensive collection of polling results on a variety of topics here, and it is kept current.
World Values Survey (http://www.worldvaluessurvey.com/)
"The World Values Survey is a worldwide investigation of sociocultural and political change. It is conducted by a network of social scientist at leading universities all around world. The survey is performed on nationally representative samples in almost 80 societies on all six inhabited continents. A total of four waves have been carried since 1981 allowing accurate comparative analysis." Find the questionnaires used. Data sets are available for analysis, even includes some online analysis.
A blog on analyzing polling data (http://politicalarithmetik.blogspot.com/) - "Political arithmetik: Where numbers and politics meet" is a blog from Charles Franklin, a professor of political science, in which he explains political bias in polls, the statistical analysis of them, and more. Provides lots of good examples and very detailed analysis.