Portal 2. Using whatever means necessary -- they don't even have to think with portals -- participants have until July 15 to submit a music video for the song on YouTube with the tag "PORTAL2NATIONALEXILE." Valve, The National and "the community" will select the winner, who'll receive a fabulous prize package of Portal 2 merch and a guitar autographed by The National.
That's all the rules, so go nuts. If you need to give the track a listen before letting those creative juices flow, check out the song after the break. If you want the full Portal 2 soundtrack, you can download that from your buddies at Joystiq right here.