I am not a huge fan of Obama. I didn't even vote for him in the primaries, and I am deeply skeptical that he will be able to make any serious change for the better. But I'm also reasonably confident that he won't make things significantly worse, which is (much) more than you can say for McCain and his frightening sidekick.
So on a practical level, I will be doing everything I can to make sure Obama wins, including spending Election Day doing get-out-the-vote work in Pennsylvania. (I've already voted, via absentee ballot.)
And let's take a moment to step back and think about the two-party system itself, which so many people seem to think is inherently evil. Our neighbor to the north, Canada, just had a national election. There were four serious candidates in the race, who were represented at all the debates, from the Conservative, Liberal, New Democratic, and Bloc Québécois parties. What essentially happened was that more than half the country voted for a more progressive government, but the Conservatives won the election since the NDP and the Liberals split the progressive vote.
Canada is, for the most part, saner than this country. Religious lunatics have little voice in government, there are actual debates involving actual issues, and corporatism is not quite as rampant. Yet their election went badly not only despite, but because of, their multi-party system.
In countries with a significant proportion of insane religious fundamentalists, a multi-party system is more frightening. It gives the crazies an outsize voice in politics. Look at Israel, where racist right-wing parties can topple governments. So whenever people bring up third parties in this country, I'm always amused that they seem to think Ralph Nadir would be a significant candidate. Hello? If this country ever gets a real third party, it's more likely to either be a right-wing religious party, or a right-wing Libertarian party. Which might help (by splitting the right-wing vote), but that means you should be hoping a third party forms on the other side, not your own.
So whatever your feelings about the two major candidates, the fact is that one of them will be President next year. You need to decide which one of them reflects your views and vision for this country, and make damn sure he is elected. Distracting yourself and others with talk of meaningless third-party candidates, is worse than pointless.