The ingenious website BotherVoting.org uses humor to encourage people to vote. On the serious side, they have resources to help you register to vote, and also help find your polling place (I would have added the site that helps you check if you are registered and the site that helps you vote absentee or early).
On the silly side, they have ecards you can use to harass your friends and ads you can place on your website. Here are two of my favorites:
