PollingReport

http://www.pollingreport.com/2008.htm   

The PollingReport complies all the polls from national surveys that are being conducted. It is an independent, non-partisan site.

National Council on Public Polls (NCPP)

http://www.ncpp.org/?q=node/4 

The NCPP sets professional standards for public opinion polls. It provides information, including an article for journalists, entitled, "20 Questions A Journalist Should Ask About Poll Results."

Pollster

http://www.pollster.com

This site allows you to quickly scan the latest trend poll trend estimates for every state in the Presidential race.

Real Clear Politics

http://www.realclearpolitics.com/polls/

This site is updated daily and provides a number of political polls for national and state levels.

American Research Group, Inc.

http://www.americanresearchgroup.com/

National polling service.

Gallup

http://www.gallup.com/Home.aspx

National polling service.

Rasmussen Reports

http://www.rasmussenreports.com/

National polling service. 

Zogby

http://www.zogby.com/

National polling service.

Pew Research Center for the People & the Press

http://people-press.org/

National polling service that goes beyond just politics.  Also see Pew Social Trends and Pew Global Attitudes Project.

Quinnipiac University Polling Institute

http://www.quinnipiac.edu/x271.xml

A polling institute that covers the Northeast region primarily.

Marist Insitute for Public Opinion

http://www.maristpoll.marist.edu/default.htm

A survey center at Marist College