I personally love my MadCatz game pad. Pretty nice quality and comfortable hold. It's styled exactly like the X-Box controller so as long as you don't prefer the Playstation style controllers it should be alright. There are both Wireless and USB(cord) models.

You are using SDL for input, correct? I can pass you my own input unit that you can take from if you want to give the option of customizable controls. In reality I think this might hurt you to leave them out as joysticks can really vary in what they have.

[size=9px]ie. X-Box style would have like 6 axis (last 2 which are used like triggers) and 8 buttons with only 1 hat. Where as PS1-3 would have (I think) 1 hat, 4 axis and 10 buttons. I'm not too sure about the Analog button or the vibrate features. They two also obviously differ in thumb placement of primary directional controls AND if it's a hat or a analog stick in the most comfortable spot.[/size]

The biggest concern is that not all the buttons are ordered the same so you might be completely changing gameplay for different controllers.