This is for smart phones, not iPad yet - not sure how well it works as I don't own one
http://www.icontrolpad.com/
http://www.icontrolpad.com/
For example, on my PC, I am using an Xbox 360 controller to play games via my USB port.
I understand that the ipad 2 doesn't have a USB port, so is there any other way of connecting a game controller to it?