If you're not voting because you don't like Bush or Kerry, the is something further to think about.
Very likely, whoever is elected will get to appoint someone to the Supreme Court, and this judge could very likely be the deciding factor in many issues which will have lasting effects for who knows how long.
I should know more about what exactly is at stake here, but the big one that I'm concerned with is the constitutional right of women to choose. However you feel on this, or on other issues that have been decided with a 5-4 majority in the Supreme Court, consider voting for the person who will likely choose a justice in your favor, if you vote for no other reason.
There's more than the next 4 years at stake whenever a SCJ retires.