U.S. Polls

Polling services are often based and operate locally and provide information specifics to local needs. For a list of polling organizations in addition to those mentioned below, see the Wikipedia: List of Polling Organizations by Country

American National Election Studies
To serve the research needs of social scientists, teachers, students, policy makers and journalists, the ANES produces high quality data from its own surveys on voting, public opinion, and political participation. Central to this mission is the active involvement of the ANES research community in all phases of the project. (source: website)
Gallup
Gallup delivers analytics and advice to help leaders and organizations solve their most pressing problems.
The Harris Poll
Harris Poll polls a representative sample of Americans of all ages, genders, income, and ethnic backgrounds regarding business, politics, sports, and health & life.
IPSOS
IPSOS provides data through polling and market analysis primarily for the private sector, delivering information and analysis needed for marketing and sales.
Pew Research Center
A valued source of statistics, facts, and trends in U.S. politics, religion, social trends, media and news, science, Internet and technology, demographics, and global issues.
Polling Report summaries
Self-described as an independent, nonpartisan, resource on trends in American public opinion.
Quinnipiac University Polls
Frequently cited by journalists, public officials and researchers, the independent Quinnipiac University Poll regularly surveys residents in Colorado, Connecticut, Florida, Iowa, New Jersey, New York, Ohio, Pennsylvania, Virginia and nationwide about political races, state and national elections, and issues of public concern, such as schools, taxes, transportation, municipal services and the environment.

Known for its exactness and thoroughness, the Quinnipiac poll is featured regularly in The New York Times, The Washington Post, USA Today, The Wall Street Journal and on national network news broadcasts. In 2010, respected public opinion polling analyst Nate Silver ranked the Quinnipiac University poll as most accurate among major polls conducting surveys in two states or more. (source: website)
Rasmussen Reports
Self-described as a public opinion polling service since 2003. Notwithstanding the "polling" aspect of the site, it seems to have a very conservative bent to its reporting.