Bit of a sidetrack...
As far as weapons go, I think the Mass Effect or Prototype alternatives are quite good ie. using a selection wheel and slowing or pausing the game while the button is held.
Though, the thing you have consider is which button you use and what you sacrifice. In Mass Effect, I believe they moved grenades onto the face buttons (the back button, I think?) and ME2 did away with them altogether. You're gonna make people select from the wheel with the right stick, and you want it a button they can hold down so it has to be a shoulder button. But you need one for firing, one for zooming in...do you want one for reloading and one for quick grenades?
I think you could probably write something quite interesting looking at certain controls for different games.