[seanwitte]

I remember seeing a two-wheeled balancing robot made with Mindstorms that used IR proximity sensors to balance instead of a gyro. We used some of the Sharp IR sensors this year, I don't have the part number handy but they're the ones with 6" - 6' range. Using one on the front and back, pointed at the floor, you can figure out your angle of tilt. They're pretty fast, you might be able to make a balancing platform without a computer, just a closed-loop with the sensors as feedback.