In highschool we had a class where the teacher would provide LEGO Mindstorms for us and let us do anything we wanted with it. Using optic sensors, we made it find its way out of a maze which we set out on the floor with tape. These things are great fun, but probably most suitable for kids to play with.

Probably a better idea would be to get started with something like an Arduino. Not too long ago I read about Tessel on HN which seemed interesting, sort of an Arduino but you could program it with JavaScript, if that's your thing.

Also there's tons of articles and videos on the web of fun projects people built with Arduino's and Mindstorms, so I would definitely google around a bit to see if you find something you think is interesting. Anyway, good luck.