I'm going to take a bit of a departure from my typical staunch Libertarian viewpoint here, and write a completely non-partisan post here.
Who should you vote for?
I can't tell you who to vote for. That is a choice you must make for yourself. In making that choice, however, you must, now more than ever, be responsible in that choice. You must learn the issues. You must realize that there are far more candidates than just McCain and Obama. You must research the issues and find the candidate that is best suited to your desires for this country - it's quite likely that it won't be either McCain or Obama.
If you're an American with the true meaning of being American at heart, you likely want to preserve the Constitution, preserve your civil liberties and human rights, and abolish the (almost) Orwellian police state that seven years of Bush Jr. has brought about. Which candidate will do that for you? McCain? Probably not. He has a voting history that has shown increased support for George W. Bush over the years, and is running on platforms that will only continue the reign of terror. Obama? You might initially answer yes, but have you researched Joe Biden, his running mate? Biden has raped (or attempted to) the American public of privacy and civil rights since the mid-1990s. He is only a name away from total fascism. That says a lot about Obama. Can't vote for Obama now? Confused? Not sure who to vote for?
Vote for the candidate that best supports your politics. VoteSmart.org is a good place to start.
Does your candidate have a chance of winning? Who cares? The state I've been living in for over 25 years is known to be wildly Democratic in elections. My state will hand Obama all of its electorates. I will be voting third party. My vote is not wasted. It is cast in protest. With enough protest votes, a message can be sent to the government that the people are not happy with the politics of the two major parties. Additionally, if more people voted with their politics instead of their party lines, a third party candidate would have a great shot at winning. If everyone I had ever heard say, "I won't vote for [popular (technically not a) third party candidate with virtually no news coverage] because he has no chance of winning," just went out and voted for the man, he'd likely be the nominee, and a major political force.
Most Americans forget that this country didn't always have Democrats and Republicans as the two major parties. Both of them were once third parties, likely meeting the same resistance third parties meet today. George Washington, our first, and greatest, president, was a Federalist. This country has also seen the Whigs, Liberty Party, Free Soil Party, American Party, and Populist party as major parties. There is no reason that a third party cannot overtake one of the current major parties.
Vote for the best candidate for the job. Don't vote for the guy you'd like to have a beer with (you'll never have a beer with him). Don't vote for the guy your party promotes (chances are, his politics will destroy yours). Don't vote for the lesser of two evils (Cthulhu has a better chance of being the lesser of two evils this time around).
Vote for the best candidate for the job. Understand the issues. Understand the way the candidates feel about the issues. Understand how a candidate's way of tackling the issues will affect you.
Don't be a moron when voting. That's how we got George W. Bush in the first place.