www.igo.com
They make a variety of charging options that use interchangeable tips to set voltage, polarity and interface.
I use a Charge Anywhere, which is a wall charger with a built in battery for charging when a wall outlet is not handy. Also two outputs, so can charge two devices at once. They also make a device that uses 2 AA batteries, for portable charging.
With iGo, I can charge my PRS600 (round plug or mini USB), PRS650 and 350 (micro USB), Palm T/X, iPhone, BlueTooth headset, and any other small devices I might buy.
Once charger, a small bag of tips.