People have laughed at me when I have told them about Legos Mindstorms. Mindstorms is a Lego computer "brick" that can control motors and sensors and is programmable. Couple that with the infinite configuaration of a set of Legos and you have an easy platform to prototype something. You may be thinking yea yea building little toys... not so!
One more.. the building blocks of any computer. 1 and 0. Logic gates! ... that's not even Mindstorm driven! Just the power of the Lego! Lots can be made with this though!
Right out of the box Dade and I were able to make a rover style wheeled robot that rolled around our kitchen floor and counted the number of black squares it encountered on it way. It would beep audibly to let us know when it found a square and show the count on it's display. These things are great brain food!