If any bike-riding hippies are reading this right now, I've got the perfect product for you. The BioLogic FreeCharge allows you to use your bicycle to keep your iPod, smartphone, GPS device, or what have you, charged up at all times. The picture shows an iPod being used, but anything you can power off of a USB hub will work.
The FreeCharge puts a dyno on your wheels that converts the energy of their movement into electricity. Your biking charges the battery within the FreeCharge, and that battery charges your device. When this thing hits in March, it'll cost $100, and BioLogic brags that it can recharge an iPhone up to full in roughly three hours.