This new CloudApp() contest looks extremely cool: the objective is to create a cloud application running on Windows Azure. There are categories for both .NET and PHP applications. The contest will be judged by Michael Cote, Om Malik, and you - the developer community will vote on a winner too.
The full details are at http://www.newcloudapp.com/.
The prizes are literally fame and fortune.
Submission are due by June 18. Good luck!