Blu e-cigarettes ran a contest with $10k up for grabs. You can currently view and vote for your favorite video at

http://viral.blucigs.com

Unfortunately, the quality there leaves something to be desired, but there are still one or two worth voting for.

I also ran across a really interesting site called Tongal, where the contest format is a little different. Usually, as a filmmaker you are blindly asked to submit content, and hope it's what the client is looking for (unless it's a popularity contest, as in the Blu contest above, in which case quality is really of the least consequence). With Tongal, there are several phases of submission, including a concept phase. Now that the concept phase is passed, filmmakers know which of the five concepts were the client's favorite, along with notes and small variations on the original concepts. That gives filmmakers the ability to shoot something with more of a focus on what will likely get picked. You can check out the contest for Jack Link's here:

http://tongal.com/project/jacklinks

Happy shooting, and good luck.