The problem: iPads don't charge through USB ports that aren't 10w. The solution: none! Sorry. But the QuickerTek iPad charge monitor at least shows how much power outflow your USB port has, and whether it's enough to charge your device.
Then again, you can also probably figure that out pretty quickly by, um, looking to see if your iPad is charging. Still, comforting to have definitive proof of your USB port's strength or weakness. [QuickerTek via Engadget]