The LP Pad controller above is from LP Accessible Technologies, due for release at the end of this month. It's a wireless Xbox 360 controller designed to be used by people with arm movement but without fine individual finger control.
Looks like a great product, although this is certainly not the only solution out there for people wanting to play first-person-shooter type games using assistive gaming technology. It's also quite expensive (although understandably) which is always a problem for access in the first place.
Added to the Accessible Gaming Shop in the "Large" section of controllers.