Votemaster looks at the numbers and finds 97 reasonable combinations that would leave the Electoral College tied at 269 votes. I won't go into all the combinations, but it's safe to say the possiblity of a tie is not too far fetched.
So, what happens if we get that result?
Turns out the founding fathers thought of this possibility. In fact, it has happened twice (1800 and 1824) that nobody got a majority. In the event nobody has an absolute majority of the EVs, the newly elected House of Representatives chooses the President, with each state getting one vote. If the state delegation split evenly, the state probably won't be able to vote. If either candidate gets 26 votes, he becomes President. However, if no one receives 26 votes, possibly due to some states being unable to vote due to evenly split delegations, then we go to Plan C. The new Senate chooses the Vice President, with each senator getting one vote. If the Senate is divided 50-50, then the President of the Senate--and on Jan. 6, 2013 when this would play out, that would be Joe Biden--gets to cast the deciding vote, presumably for himself. If on Jan. 20, the House still hasn't chosen a President, the new Vice President would serve as acting President until the House got its act together. The deadlock could be broken by a House member switching parties (and you can imagine the wheeling and dealing that might occur to encourage that), a member dying, or if it got that far, the 2014 elections.
Suppose the electoral votes are tied, nobody gets 26 votes in the House, the Senate is tied 50-50 and Joe Biden has died after the old Senate has permanently adjourned. President Obama would instantly nominate a new Vice President, but the hamstrung Senate would never confirm him. At that point there would neither be a President elect nor a Vice President elect, so the new Speaker of the House would become President and in his or her absence the President pro tem of the Senate (Daniel Inouye at present). After that it gets hairy. Normally the Secretary of State comes next, but her term would normally end on Jan. 20, 2013 so it is unclear what would happen after that. Probably if all this happens, the Supreme Court would get into the act. Hopefully the electoral college won't be a tie.