I think the Pew Research Center for People and the Press is one of the best resources out there for finding “non-partisan” survey data and polling.  The sample sizes are large, extensive, and peer reviewed.  According to their website:

The Center’s purpose is to serve as a forum for ideas on the media and public policy through public opinion research. In this role it serves as an important information resource for political leaders, journalists, scholars, and public interest organizations. All of our current survey results are made available free of charge.

They have a new report detailing “Trends in Political Values and Core Attitudes: 1987-2007”.  My favorite part of the survey is below the fold…

Even more striking than the changes in some core political and social values is the dramatic shift in party identification that has occurred during the past five years. In 2002, the country was equally divided along partisan lines: 43% identified with the Republican Party or leaned to the GOP, while an identical proportion said they were Democrats. Today, half of the public (50%) either identifies as a Democrat or says they lean to the Democratic Party, compared with 35% who align with the GOP.