The APC UPB10 (about $60) is a handy little battery that is charged from and charges over USB. It is the size of a deck of cards and is very useful if you need to finish that game, movie, or phone call when you are away from a power outlet.
The APC UPB10 more than doubles the power to an iPhone, Blackberry, or Sony PSP. It charges any USB device, which also includes some GPS devices and cameras.
It does require you to push a button to activate the power. If the device you are charging is nearly out of power, the APC will continue to charge it. If the device is nearly full, the APC will only charge it for about 20 minutes before you need to press the button again. It does this to save the battery.
If you are like me and sometimes find yourself on the other side of D.C. without any cell phone power left, the APC UPB10 can help.