So a few months ago, I stumbled upon a thing at Adafruit.com called a "Charger Doctor" which was really just a Multimeter designed to slip inline with your USB cable. It was $7.50 and I liked it.
Seattle, Wash. — Signametrics Corp. has introduced the SMU2055 6-1/2 digit USB digital multimeter (DMM). The SMU2055 is powered directly from the USB connection, and consumes only 1-1/2 watts.