Cubelets – modular robots

Cubelets Engineering Prototypes from eric schweikardt on Vimeo

The standard kit of cubelets has 20 blocks and contains an assortment of sensor, action, and operator blocks. With it, you can experiment and create mobile robots and logic constructions.

Really cool idea. I would love to buy a set of these but $300 is more than I can afford just now, plus they're out of stock and seem to only be available on request.