MakerBot's just released three open source hardware toy kits to produce with your 3D printer: an RC car, a windup robot, and a hand-cranked dynamo:
The MakerBot Botmobile is the first open source remote control car. MakerBot's own designer Michael Curry, took everything he learned from creating the Turtle Shell Racers which were featured on the track at Maker Faire, and created the Botmobile kit. All you need to do is get the kit, print out the parts from thingiverse and you'll have your own RC car. It's got a great 12 volt motor, a 2 channel radio controller, a tiny servo for steering, rubber racing tires; all rolled into a a ready-to-go kit. The BotMobile kit requires no soldering, all the parts snap together – It really is a perfect weekend project. The body design is a slick dune buggy – and it's already on thingiverse (link), ready to be printed. You want to change it or customize it? The design files are open source and are ready for you to turn it into a hot rod.