Instructables has an interesting article on building a bicycle powered USB generator so that you can charge or run USB driven devices (like your iPod, Garmin, etc) while you are pedaling through the city (or countryside as it were).
“The basic idea for the USB Bike Generator is to use a suitable stepper motor as a generator and a voltage regulator circuit to maintain the 5 volts needed for the USB ports. In this instructable I will show you how to build this generator and through testing show that it is 70% efficient at converting the power from the generator to the power needed for the USB port. “
Sounds cool, I’d be interested to see how it works in practice. Keep in mind also that, as with most all Instructables, the comments section is as important and enlightening as the article itself.