General prediction: The Republicans will pick up
This is actually a good outcome for the Republicans. Even if they were to gain a majority in both houses of Congress, they still wouldn't be able to get anything done. Obama has a veto pen. But if they get a majority in even one house, Obama will be able to lay on the "Republican obstructionist" stuff more thickly and more credibly. Remember, Bill Clinton's numbers went up after the 1994 "Republican Revolution." Remaining in the minority now boosts Republican prospects in 2012, because they can spend the next two years forcing the Democrats to accept ownership of everything that comes (or doesn't come) out of DC.
Alaska: Lisa Murkowski will become the second American, after Strom Thurmond, to be elected to the US Senate by write-in vote.
Arkansas: Not even getting caught in bed with a dead girl or a live boy can stop Republican John Boozman from unseating incumbent Democratic Senator Blanche Lincoln.
California: Incumbent Democratic Senator Barbara Boxer will be re-elected. Not by a huge margin, probably, but she'll pull it out. It's not so much that Democratic gubernatorial candidate Jerry Brown has coattails for her as it is that his Republican opponent, "NutMeg" Whitman, has negative coattails for GOP Senate nominee Carly Fiorina.
Colorado: This state will be a GOP pickup as Ken Buck unseats incumbent Democratic Senator Michael Bennet.
Connecticut: Democrat Richard Blumenthal bests Republican Linda McMahon for the state's open (due to Christopher Dodd's retirement) US Senate seat. As with California, this won't be a blowout. It may even be a nail-biter (Blumenthal's lead has been shrinking for some time). But it's just not going to happen for the GOP there.
Delaware: Sorry, guys, Christine O'Donnell isn't going to win. Chris Coons holds Vice President Joe Biden's former US Senate seat for the Democrats.
Florida: A few months ago, I'd have picked Republican governor Charlie Crist to win this US Senate race as an independent. I was wrong on that. Republican Marco Rubio has it pretty much in the bag.
Illinois: The polls show Democrat Alexi Giannoulias and Republican Mark Kirk in a tight race for the US Senate seat formerly held by President Barack Obama and currently filled by Roland Burris. Don't believe the polls. There's no way the Democrats are giving up this seat, even if the dead have to rise and go to the polls to help them keep it.
Indiana: Another Republican pickup, with Dan Coats beating Brad Ellsworth to replace the retiring Evan Bayh.
Missouri: Republicans will hold on to the seat being vacated by retiring Kit Bond. As disgusting as the GOP nominee, US Representative Roy Blunt, may be (however tall he is, I didn't know they stacked shit that high), I can't really blame Missourians. The Democrats managed to find and nominate Secretary of State Robin Carnahan, one of probably only three politicians in Missouri less popular than Blunt (of the other two, Claire McCaskill was busy being a Senator already and former Governor Matt Blunt didn't run against Dad).
Nevada: Incumbent Democratic Senator Harry Reid will beat Republican nominee Sharron Angle like a drum.
Washington: Incumbent Democratic Senator Patty Murray will beat GOP nominee Dino Rossi.
I think the only even nominally competitive race I'm leaving out there is DioGuardio v. Gillibrand in New York. It doesn't look that competitive, and I'm betting it's even less competitive than it looks -- Gillibrand in a walk.
So, like I said,
Update, October 8th: FOUR! FOUR GOP PICKUPS IN THE SENATE! I was just looking back over this post, and jumping Jeebus, I spaced an entire state, and an important one -- Wisconsin. Big brain fart, and I have no excuse or explanation for it. If the current polls and the trend are right, and I think they are, incumbent Democratic Senator Russ Feingold will go down on November 2nd to be replaced by Republican challenger Ron Johnson.
Feingold's scalp is probably the most prominent one that will get mounted on the GOP's trophy wall this year. He's high on the Republicans' hit list (for good reasons, including "McCain/Feingold") and low on the Democratic Party's support list (for bad reasons such as the fact that he didn't stop talking about torture, civil liberties, etc. once his party took the White House and commenced Bush's third term). Them's the breaks.