Not sure about portal, but I've used a PS3 controller with software that emulates xbox 360 controllers. It was fairly difficult to get set up and then running every time but once it was running it was rock solid. Played my way through Lara Croft: Guardians of the light with it.

I think it was this: http://motioninjoy.com/download

I found that my Logitech RumblePad 2 worked great out of the box, and even better (almost flawless, the 360 controller has one extra button) after going through the button mappings in big picture settings.

Which is fine by me, it's one of the better gamepads I've used in a while and its widespread adoption makes for good prices and speaks well for future use.