Silverlight Tetris
I decided to do a Tetris game with a slightly different appearance than the standard square blocks. This Silverlight Tetris game uses translucent cubes, utilizing a Silverlight 3D library which I developed for the Silverlight 3D Dice Simulator I wrote. This library allows a scene containing 3D polygons to be built up and then rendered to a 2D Canvas. I was planning all sorts of rotation effects and shading for the Tetris game, but in the end, I had to simplify things because Silverlight couldn't calculate a full grid of 3D cubes quickly enough (the grid is 23x16, and each cube has 6 sides, so there are up to 23 * 16 * 8 = 2944 polygons each with four vertices...). So in the end I settled for some subtle lighting effects on the blocks, and 3D rotation for the next shape display.
Still, I think it's pretty nice. It definitely has that mind-numbingly addictive effect you would expect from a good Tetris clone.
If you're interested, you can download the Silverlight Tetris source code.