RealClear Politics has a nice listing of the latest poll results. The analysis is a bit biased towards the GOP, but you can find the raw poll numbers there.
If I had to guess, I think the final numbers will show the Democrats will do better than the polls suggest – simply because of the fact that, in the last election, polls showed Bush ahead of Gore by several points on the eve of the election. I think there is the same potential for a statistical bias in the same direction in this election as well.
RealClear Politics – Congressional Races