I’m the type of person who absolutely must disassemble just about everything I can get my hands on. (Carla still tells folks about me taking apart a small battery operated truck I received for some single digit birthday — before we even left the parking lot of the post office!) Few things amuse me more than magnets and gears, but this video of non-circular gears (found on MAKE really bent my brain!
If you watch to the end, or click straight through to YouTube for related videos you’ll find that there are tons of cool gear videos including some nice Lego projects.