"I Voted" Badge
I've accepted that I probably won't score the cool new NASA badge that Toni wrote about. Not to worry because there is a special badge that you can unlock on Tuesday, November 2, 2010!
All you have to do is Check-In at your polling place on election day and you'll unlock the "I Voted" badge. It will only be available on that day, so it's definitely something to brag about.
(If you voted early or by mail you can still get the badge by shouting "I Voted" throughout the day).
Here's a link to the official Foursquare blog post for more information: http://blog.foursquare.com/2010/10/28/check-in-and-vote-on-foursquare.