John Dickerson at Slate posts an extremely helpful guide to watching tonight's returns, and the things to keep an eye out for.

Highlights (all times EST):

6pm: First polls close

7pm: Polls close in Virginia and most of Florida

7:30pm: Polls close in Ohio and North Carolina

8pm: Polls close in Pennsylvania

By around 8pm, we should have a reasonable idea of where this election is going, and some key Senate races, if not a clear idea of who the next President will be.