This is probably the best site for seeing all the polls in one place. The guy who runs it is one of the big whigs at Baseball Prospectus and is huge on statistics. He's behind some of the new age stats that managers and GMs are using more and more.
So he's taken it to politics now and ranks/grades polls based on their previous performances and other factors. He uses data on party ID, age, etc. He then runs 10,000 computer simulations of the race each day to determine his data. He was remarkably close during the primaries.
If you're a political junkie, this is a pretty sweet site.
http://www.fivethirtyeight.com/