Film4Prizes is a cool site that maintains a database of several online film & video contests which include many with cash prizes. Here are a few interesting contests that they list:
– “HP You On You Contest” – top prize is $40,000.
– “Nobody’s Gonna Lay a Finger on My Butterfinger” Video Contest – top prize is $25,000.
– The Reason Project video contest – $10,000 top prize.
Their database is sort able, so you can choose which contest suits you best. Definitely worth checking out.