I am looking for a charger for my new PB. I stumbled upon this: CrazyOnDigital Sync and Charger Dock Cradle. I know of the BlackBerry Charging Pod for PlayBook from RIM, but this is a bit more cost effective and has usb.
It looks to me like that one charges only through the USB port. Personally I'd be concerned about how fiddly it seems to me it would be to plug the tablet into a cradle using the USB port.
I also wouldn't buy it without learning the exact output specifications (voltage/current) so I'd know it was actually going to charge at a reasonable rate. I wouldn't expect it to have as much extra charge capacity as the rapid chargers, so it would likely not charge very quickly if the tablet is on while it's plugged in here.