In the Senate, Virginia (1am-2am), Montana (4-5am), Rhode Island (3-4am) and Missouri (2-3am) are the ones to watch. Democrats also have to win Ohio and Pennsylvania and hold New Jersey and Maryland. I am assuming Tennessee will stay Republican.
Pollster Del Ali goes a little further on the early House seats to watch:
There are three congressional races in Indiana worth watching: IN-2, IN-8 and IN-9. If two of the three go Democratic, the Democrats will take back the House. If all three go Democratic, its "Good Night Irene" for the GOP.
It's the same situation in Connecticut when looking at CT-2, CT-4 and CT-5. If one of the three go Democratic, it's a good night for them. If two of the three switch, read above.
I have distilled the above from various postings on Political Wire, which has an excellent list of links for tonight.