http://www.engadget.com/2011/04/06/sanyo-eneloop-mobile-booster-provides-79-of-stateside-usb-power/
Sanyo has introduced a portable rechargeable power supply for devices that can accept 5V DC via a USB cable (these days, that includes most small recorders). The battery holds 5000 mAh, and can provide 1000 mA to a single device, or 500 mA to each of a pair of USB-attached gadgets.
that looks pretty cool.