Objet, one of the major manufacturers of commercial 3D printers, is offering a complete car at no charge. Well, it's not a *real* car, it's only a 3D model of one. You can find it at the link below.
Objet produced this model to demonstrate the capabilities of their 3D printer line. What are they demonstrating, exactly? This very small model (2cm in length) has some very unusual features in a 3D model, at least for home 3D printer operators.
We suspect you won't be able to print this model at home on your (MakerBot, BFB, Up!, RepRap, Ultimaker, etc) because it has a complete set of moving wheels and axles. Theoretically if your printer has sufficient resolution and an ability to print non-contiguous shapes with support, you'll have a teeny car that rolls on its own.
But maybe we're wrong. Please give it a try on your device and let us know if it works.