My own electoral college model has us at an exact tie again today. Given that, it seems like a good time to highlight what 538 is saying about this right now as well:

12th Amendment Update: Tie Probability Continues to Increase
(Nate Silver, fivethirtyeight.com, 19 Sep 2008)

The latest in our occasional series informing you about the country’s worst nightmare: a 269-269 Electoral College tie…

As you may have noticed from our scenario chart, the probability of a tie has increased dramatically in recent days and now stands at 3.2 percent. This is partly because, as we draw closer to election day with the race remaining tight, the probability of any one candidate running away with the election diminishes — meaning that all “close” electoral permutations, including ties, become more likely.

However, there is one specific scenario that is driving this outcome. That is the scenario wherein Barack Obama wins the Kerry states plus Iowa, New Mexico and Colorado, but loses New Hampshire. Of the 320 times that our simulation ended in a tie, this particular scenario was responsible 294 times. Indeed, we presently have Obama winning precisely the Kerry states plus Iowa, New Mexico and Colorado, so all that would be needed to make a tie occur is to flip New Hampshire back to McCain, and entirely reasonable possibility.

…

By the way — the way that the tipping point math works out, about 80 percent of the tie outcomes involve McCain winning the popular vote. This is by far the messier of the two scenarios. Since the Democrats will almost certainly control a plurality or a majority of House delegations in the incoming Congress, a tie accompanied by an Obama win in the popular vote will lead to a lot of fanfare but ultimately little drama — Obama will become the next President. But if McCain wins the popular vote, there will be far more pressure on Democratic Representatives to vote against their party.

Nightmare? Come on, it would be even more fun than 2000. I couldn’t possibly be so lucky as to see two such cases in a lifetime, could I? It would be a blast!