Not to be out done by the recent flurry of convention announcements, The Blizzard World Wide Invitational 2008 is throwing out an announcement or two of its own. Today, they are officially announcing a Machinma contest. There will be two categories, one for movies, and one for TV Commercials for WoW items. Online submission is open from June 9th to June 16th. You can check out the contest details (Including the prizes, of course) here.
If Machinima isn't your thing, but you're still creative in other arenas, the announcement also mentions that they will reveal more contests in the near future.