Brother (the printer/sewing machine company, not my brother Frank), has developed vibration-powered batteries that promise to stay charged simply by shaking them. Shake Weight battery chargers? I think so!
Called the Vibration-powered Generating Battery (maybe in the future we'll all ask for VGBs instead of Energizers), the batt's fit in any regular ol' AA or AAA slot. Of course, there are already plenty of rechargeable alternatives out there -- and most gadgets today just use lithium-ion batteries -- though you still need to plug either in if you want to get some juice. With vibration-powered batteries, you'd be able to charge up anywhere, anytime.
Okay, so typically I don't share my scientific discoveries with anyone, but this one's just too good to keep to myself. So check it: you take a bunch of these batteries, and you jam them in a vibrator. Boom -- PERPETUAL. F***ING. MOTION! Double entendre, count it!