President: Mitt Romney. Vice-President: Joe Biden

It could happen.  An article in the Los Angeles Times explains how:

As I put together different combinations, I had in mind that Republicans traditionally do pretty well in most of those states still too close to call. So, I hit on a scenario that gave Romney the southern trio -- Virginia, North Carolina and Florida -- plus the two Western states – Colorado and Nevada – that are seldom hospitable to Democrats. I also gave Romney Iowa in the heartland, although that is pretty good ground for Obama. To the president I gave only Ohio as a reward for saving the auto industry and New Hampshire because, in the end, that independent little state generally goes for the Democrat.

It was a completely plausible split and the result was a shock: 269 electoral votes each for Obama and Romney. A tie! As those of you who paid attention in social studies class will remember, if no candidate achieves 270 electoral votes, the decision is thrown to the newly elected House of Representatives. There, each state gets one vote...

That means an electoral college tie puts Romney in the White House. But the news is not necessarily as good for his running mate, Paul Ryan. The Senate gets to pick the vice president, and each senator gets one vote. If Democrats hold on to the Senate this fall...

President Romney and Vice-President Biden.  God help us.  And this final note:

Of course everything changes if just one elector in one state takes it upon himself to break the tie. In most states, that would be a perfectly legal thing for an elector to do. Such craziness is the risk we run under a system in which every vote counts, but some count a lot more than others.