I missed the mark on this one, but thanks to a recent posting from Dino Esposito, I just became aware of ComponentArt’s 2009 Summer Silverlight Coding Competition. 

The best application (as selected by the panel and community votes) will win $10,000, and two-runners up will receive ComponentArt licenses.  Use of ComponentArt products is NOT required.  Applications will start appearing for community voting today, but you have through September 22 to submit your entries.