Thanks for the replies - I ended up buying the Logitech G13 and I am EXTREMELY happy with it. Yes, it is large, but being that the idea is to get the main keyboard out of the way, that really isn't an issue for me.
To the last poster, I think you are missing the idea here; that being to replace the keyboard, not the mouse. If I wanted to control my gun with a D-pad, I would have kept my PS3. No, my gripe is that of using a big clunky keyboard for the use of just a handful of keys. These left hand controllers are the cat's ass: ergonomic, customizable, and just plain easier to use.