With white LED lights in each foot, these Minifig flashlights are all kinds of cool. Crank the not-so-Minifig version's arm to keep him lit, or pick up the battery-powered keychain to help get your keys in the door.
Whether the laws of physics would allow something like this to happen, I do not know, but Jin Woo Han's faucet dynamo concept for powering small electric devices with water power is a neat idea.
In rural Africa, electricity is hard to come by. That's why Dr. Cedrick Ngalande has developed the Green Erg Generator—a dynamo that produces electricity from friction generated with the ground while walking.