We’re looking to start some development which will require USB Host functionality on Android. We were going to use the Samsung Galaxy 10.1, but this question suggests that Samsung have removed this api.
What tablets definitely have this working fully?
The US version of the Motorola Xoom Wifi-only (MZ604) is your best shot. This is a GDE (Google Device Experience) which means that it is a clean Android version. In other words Motorola has not done any modifications to Android and the USB-host API is intact.
Check my thread on the motodev forum.