Why don't you try a nice Silverlight game on Facebook?
Our dear friends in Plexipixel have created a nice Silverlight based game on Facebook. It is called Roshamboom! (http://apps.facebook.com/roshamboom).
Roshamboom! is inspired by David C. Lovelace’s extreme rock-paper-scissors concept called RPS-101. The RPS-101 (http://umop.com) game got a ton of web chatter when it was released back in 2007 because it took David over a year to concept the game and produce the 5000+ outcomes. The Plexipixel folks thought it would make an ideal (and silly) turn-based game for Facebook. Plus, it allowed them to practice some Silverlight skills. You can read more about the game here: http://plexipixel.com/blog/2009/04/roshamboom-how-it-came-to-be.html
Try it and let me (and the Plexipixel folks) know what you think.
Barak