This comes from DailyKos, but I still think it's a useful tool for Romney supporters and advanced poll watchers alike.
Basically this is a series of charts showing the major counties in each state along with a) the percentage of the state vote each county represents, b) How much Obama needs to get to 50% in the state, and c) How much Obama got in that particular county four years ago.
As this is likely to be a squeaker in most of the swing states, these charts will essentially allow you to do rudimentary calculations on where the vote is headed even if the state itself has yet to be called. It's not unlike what John King does with the Magic Wall on CNN, but easier to track minute to minute.
I'll be using these charts along with CNN's county by county numbers (they do the best job updating the numbers, imo) all night to see where things are. The margin in Cuyahoga County in Ohio will be focused on particularly hard, but as Virginia is the first swing state to close it's polls completely, the margins in Fairfax (14% of Virginia's population, won by Obama 60-39 in 2008 but only necessary to win 57-42) and Virginia Beach (5.4% of Virginia's population, won by McCain 50-49... Obama needs at least 46% to win the state) counties will give us the first inklings on where this night might be going.