Fun Silverlight Game: Crayon Cannon
Kudos to the Popfly team for adding new features in their July update. My favorite features are the pre-loading of assets which will pre-load images, audio, video before a game starts so it doesn't lag out and the High Score service. The full list of features can be found on the Popfly Team blog.
If you haven't played this game, stop what you're doing and give it a try. It reminds me of Crayon Physics Deluxe in its simplicity and addictiveness.