For those, like me, that hate the gamepad for first person shooters on the Xbox, there’s the XFPS.  There’s quite a few reviews out there and I had given up on finding something, but I may end up giving this a try!    My Wolfking Warrior XXtreme may be perfect.  The one item that bothers me with the DriverHeaven review is their bad point (obviously):

Allow some system to adjust the mouse sensitivity as not every 360 game lets you change the thumbstick sensitivity, this can cause issues with games requiring fast 360 degree movement.

Anyway, check out DriverHeaven’s review.