(Video Link)
Benjamin Krempel founded a company called PumpTire, which is marketing a rather unique bicycle tire. It has a partially open tube on the outer circumference. As the wheel turns, it opens and closes the tube, which draws air from the outside and pumps it into the interior of the tire. When the tire reaches maximum pressure, it shuts off. In a test ride featured in the video, the tire inflated from 22 to 52 psi after three and a half minutes of riding. Link -via DVICE
Seems like this will work best for large, low pressure tires.