Supervirals.com (terrible name made worse by the logo) is a new venture that allows brands to brief out "viral video" in exchange for prizes. They've signed up mambo, Krispy Kreme and Nudie juice so far.
They describe themselves better than I can so this is form their FAQ section
"SuperVirals is a new creative platform where you can win big prizes by creating and uploading original ideas for sponsor brands. Which means it's also the place to see the best new viral content on the web!"
The briefs are open enough to allow creative freedom but my cynical view on the world won't be banking on this taking off. It just feels too labored?. But I've been wrong many times before. I think 1% (read here) sums it up well.
All comps require the user to sign over all IP with their winning entry. I guess this matter little to the general public but matters a lot to people who actually have talent.