The national media has been foaming at the mouth for weeks about a Democratic takeover of Congress. My general consumer advice is to discount the MSM's optimism. There will be Democratic gains, but the GOP will hold the Senate and maybe the House.
The most level headed information and opinion can be found here. One of my favorite analysts, Jay Cost, says that well-known prognosticators Stuart Rothenberg and Charlie Cook are overstating their own data fairly dramatically. His theory is that they'd rather make sure they catch any big wave and if they miss, they'd rather err on the Democratic side. He has the numbers to back up his theory.
If you think Cost is blowing smoke, consider this -- on election night 2004, I stopped watching network news and instead went to Cost's blog, which was correctly predicting Bush victories in Ohio and Florida and was saying why based on the early returns. Cost had predicted wins in those states days before the election by analyzing new registration patterns. While most of the MSM was waffling on those two states, he was very sure of himself and was spot on.