We actually did the modifications to a playstation 1 controller. Opened it up, scrapped the circuit board inside, and etched our own. It didn't drive the bot (in the analog sense, we used the joysticks for that), but the custom button placement did control a number of functions, from ball pickup, to 2x grabber control, to arm deployment. It was sort of cool, although after all the mods, it didn't look too much like a playstation controller (other than the general shape), but it worked well in lieu of a classic black box control system.
IMHO, there's not much that can top the old style CH joysticks in terms of control- tight enough to get the robot where you want it, when you want it, but loose enough to allow the robot to flow. Very simplistic buttons too, top, trigger. Can't go wrong
