Edison Media research has posted a guide to covering Election Night, which includes the following handy listing of when polls close throughout the night and the corresponding electoral votes that will be decided at those times:

7:00 PM - 58 EVs
7:30 PM - 40 EVs
8:00 PM - 171 EVs
8:30 PM - 6 EVs
9:00 PM - 159 EVs
10:00 PM - 20 EVs
11:00 PM - 81 EVs
1:00 AM - 3 EVs

All times Eastern. Hat tip: The Corner

Update 11/2: For those coming from Edison Media Research, be sure to check out the TTLB Election Resource page, with links to a wide range of election-tracking resources which can be displayed as a sidebar in your Mozilla or IE browser.