RCP is great blog, and they also do a nice job of tracking polling stats. They don’t update as often as some of the tracking sites, but they do organize it well, and have a nice flash based “RCP Graph” for both the Republican & Democrat races.
A current summary – Clinton won the nomination, Edwards et al. need to get over it and move on. Thompson surges on Guiliani, and most polls have ‘the big spender’ beating Guiliani by about 3 points. Click on the “general election polls” and the “RCP Chart” links on the side to see the graphs.