Chess in Silverlight 2
The Silverlight folks have created a chess-playing demo in Silverlight 2.
The game is here: http://silverlight.net/samples/sl2/silverlightchess/run/default.html (credits and other samples here)
Now, if you're a bit bored, you can try something mildly amusing. About half-way through the game, as the .Net side is moving in for the kill, click on the player buttons at the bottom and top to switch which implementation is playing which side. It can be interesting to watch the .Net implementation start trying to dig its way out of the hole. In most runs that I tried, it was usually able to pull out a win (though in one case, it was only able to force a stalemate).
PS. You'll need to install Silverlight 2 from here, if you don't have it.
Updated 12/18/2008: Updated the post to the Silverlight 2 version (it used to refer to 1.1 Alpha, which was renamed to 2.0 when it shipped)