Yamaha sells this wall-outlet charger that has a USB port on it designed for
their BODiBEAT MP3 players. Its just a standard USB port, though, so it can
be used for anything. I'd personally trust this more than some random
charger from ebay or dealextreme, and its a good price:
Yamaha BODiBEAT Power Adapter - $0.84: http://www.amazon.com/Yamaha-BODiBEAT-Power-Adapter-Black/dp/B0