The REGEN Yo-Yo powered MP3 player was the winner of the recent Pop Sci and Core77 challenge to develop a human powered device.
According to the product description, “between 10-12 tosses per hour are sufficient for continuous music play. A wireless (bluetooth) headset allows the user to listen to music while yo-yoing. Storage capacity of up to 200 MP3 songs on flash ROM (the equivalent of 15 CDs).”
At this point, the REGEN is only a prototype and no plans for commercial sale have been announced. Still, the concept is interesting and it seems likely that it would end up on store shelves sometime in the near future.