Chances are, if you are human and you are alive, you spend a lot of time breathing. Turn that breath into power for your USB devices with this DIY charger.
You can use this DIY charger to juice up your USB devices with any exercise (except swimming... we wouldn't recommend using this when swimming). Or, if you're not the exercising type, you could even use this while sitting around and playing video games... though if you're just sitting around the house, we expect you'd have a wall charger nearby anyways.
The guide is very well done, noting exactly how this model was built, but offering suggestions for other versions. This particular one was built out of gears and motors from old CD drives, but you could in theory use anything you want — in fact, the better the motor you use, the more charge you'll be able to eke out of your device. Just like the bike hack, you'll need some soldering chops and no fear of working with small electronics, but it's a pretty neat hack from which you can springboard your own ideas. Hit the link to check it out.
Breath Powered USB Charger [Instructables]