The one I would recommend and it also has the best performance is the Microsoft Wedge Keyboard. You can find it in the Microsoft online Store.
In general, almost all Bluetooth keyboards will "function" to include those designed for iPads. They do not have good performance and I have two of them myself. The only one that did work good was Apple's aluminum Bluetooth keyboard.
The Microsoft Wedge Keyboard has a hard rubber cover that when removed, turns the keyboard on and the cover is hinged in the middle so that you can fold and shape it into a stand for the tablet. When finished, you put the cover back on and it shuts off the keyboard.
USB keyboards; all of them work. I have a dozen of those things and all of them worked to include one that has a touchpad similar to a laptop keyboard.
Wireless keyboards will also work and I have two of those and have tested them on my RT.