The "big three" states to watch are Virginia (polls close at 7 PM EST), Pennsylvania (polls close at 8 PM EST), and Colorado (polls close at 9 PM EST).
Here is the hour-by-hour breakdown of when polls close--along with some of the more important comments by Silver. Of course, for all the details you'll need to read the whole thing.
6 PM EST. Polls close in portions of Indiana and Kentucky.
7 PM EST. Polls close in Virginia and Georgia, as well as most of Florida and most of New Hampshire. ("Virginia, for my money, is the most important state in this election. If John McCain loses it, his path to victory is exceptionally narrow—he would need to pull out an upset in Pennsylvania, while holding on to Florida and Ohio, and avoiding a sweep out West.")
7:30 PM EST. Polls close in Ohio and North Carolina.
8 PM EST. Polls close in Pennsylvania, Michigan and Missouri. ("Pennsylvania in particular is the one to watch. If Barack Obama holds onto Pennsylvania—the only state where John McCain seems to have been closing the gap over the last week of the campaign—then winning virtually any red state [Virginia, Florida, Ohio, Colorado, Missouri] would probably clinch the election for him."9 PM EST. Polls close in Colorado, New Mexico, Wisconsin and Minnesota. ("Colorado, meanwhile, is the last of what I'd characterize as this year's "Big Three" states [the others are Pennsylvania and Virginia]. If Pennsylvania and Virginia have split their votes [and Obama hasn't picked up Ohio or Florida], then Obama probably wins if he wins Colorado, and loses if he doesn't."
10 PM EST. Polls close in Nevada, Iowa, Montana and New York. ("This is the earliest point at which the race might be officially called for Barack Obama—there just aren't enough electoral votes out there, even if he's swept every swing state, to get him to 270 until New York's 31 come in.")