I have to add one more reason to Kungfuramone's excellent list of reasons to vote.
1. Pick someone that votes the opposite of what you do and then classify your vote as a "cancellation" vote. For instance, I am always especially motivated to vote so that I can cancel out my dad's vote. I get special satisfaction from this because he is one of those people that you cannot persuade, sway, or enlighten once he has made up his mind. So in effect, his vote for the Republicans is cancelled by my vote for the Dem's, ha ha ha (maniacal laughter as I mark my ballot). There are plenty of people out there whose vote needs a good cancelling - whose will it be?
Disclaimer - I really like my dad - I just don't talk to him about politics.