Well, if you insist on using one I would imagine any pad should be fine. users preference me thinks!
However, the same way FPS on consoles are designed to be played with a pad, they are designed to be played with Kb/M on the PC.
There may simply be no way to use a pad if the game doesnt have the settings for it.
I recomend you learn how to play with a good mouse and keyboard. Once you get used to it, you wont want to go back to using a pad for FPS. (Trust me I used to be the same!)
Try a belkin nostromo . Not a control pad more like a small keyboard with a handy cursor pad under your thumb for movement and a multitude of nicely placed keys and buttons under the rest of the fingers.
Bad news is: it only comes in a right handed version ( left hand on pad , right hand on mouse).