You can check out a bunch (if not all) of the short films that played at Sundance on their website. I've only watched a few so far, but here are some of my favorites are:
-The Pity Card (directed by Bob Odenkirk, about the effects of a guy taking a date to the Holocaust Museum)
-Robin's Big Date (starring Sam Rockwell as Batman and Justin Long as Robin)
-Ha Ha Ha America (don't even know how to describe this)