I just installed the shelf the monitor is sitting on and thought I'd show it off. It's the slide-out keyboard tray from the desk. I took off the metal bits on the side, installed a couple of shelf brackets underneath it and voila!
The reason for this is that my monitor has the most epically unstable stand. Typing 'hard' on the keyboard would jiggle the monitor and I couldn't be bothered with it anymore. The screen is awesome, terrific image reproduction, but you can get less jiggling going on at a Jamaican midnight party.
An additional benefit is that I can still hide away my keyboard, which slides perfectly underneath the new monitor shelf.