I don;t know if I've memed Hack-a-Day before, but they are a great hardware hacking site. Anyway this projects takes lets you use household batteries to charge protable devices that can be charged over the USB port (like my cell phone and iRiver).

Really simple design. Using a voltage regulator, you drop a 9V to 5V, and attach it USB female connector.

DIY USB 'Battery' charger