I just got a Digipower JS2-PCAM this evening from Best Buy for $17. It's a portable usb charger rated at 2200mah and 5.5V at 1000mA. It weighs only 2 ounces. If it's as good as the specs then it should be awesome for powering the hd 808's that I run.
I'll update this thread when I test it out some tomorrow.