According to Electoral-vote.com:
If the Senate election were held today, the Democrats would take control of the Senate, 52-48 (counting independent Sen. Jeffords as a Democrat, since he caucuses with the Democrats). And this realignment does not take into account the possibility that Sen. Lincoln Chafee (R-RI) might pull a Jeffords and jump ship. He is from a hugely Democratic state and, like Zell Miller, would be much more appreciated in the other party.
They're all fairly close races, though, so get out there and canvass! Let's give Kerry a Senate to work with!