Microsoft is running a couple interesting contests for application builders:
Mash-it-up with “Atlas” -- build a mash-up application using Microsoft's "Atlas" Ajax technology, and win an Xbox 360.
Made in Express Contest -- build an application using one of the (free) Visual Studio Express tools, and win $10,000.
I've got a bunch of ideas for stuff that would be fun to build for these contests. Now if only I had some time!