Andrew Gelman makes an argument for the rationality of voting (against some resistance). Here's my personal take on this. If I did not vote I'd feel guilty about failing to discharge a basic obligation of citizenship; hence voting, in my case at least, avoids psychic pain. It also gives some, albeit small, psychic pleasure as a form of self-expression. Avoiding pain, gaining pleasure: what could be more rational? Cue Jeremy Bentham.