Yet another cool thing to do with a WiiMote: Build an electronic multi-touch whiteboard.
The WiiMote includes an infrared camera which can be used to track points which reflect infrared light. Johnny Chung Lee used this feature to work with self-made infrared pens on various surfaces (primarily projections):
The descriptions sounds as if it should be relatively easy (and cheap) to build something like that yourself. All necessary software is available on Johnny’s website.