Before Android 3.0, Honeycomb, Android lacks support for any HID bluetooth keyboards. Now with the 3.0 update, Android can easily sync up with most HID keyboards.
If your Android tablet or smartphone have a usb connector, then it would be capable of using usb devices, just like the plug and play feature of Windows.
For any devices before Honeycomb, there is the Freedom Pro Bluetooth Keyboard. This bluetooth keyboard has generally good reviews, with many loving its unique features. On the other hand, others say that the device lack instructions for installation and usage.
I am sure everyone would agree that physically, it could a more modernized design.