I have a Galaxy Tab 2 7.0 and recently bought one of these
on Amazon, which has 3 USB-2 ports, SD(HC) and TF slot, and MS/M2 slots which I don't use at all. It works with USB drives, a 32GB micro SD (TF) card I had, and my USB keyboard, including supporting the media keys for volume and play/stop.
The USB cable works as a MPT device, not a USB drive, which is fairly standard, I believe. It requires a special driver, available for windows and Mac. For Linux, it doesn't seem to be recognized by the OS, but Calibre seems to recognize it OK.