Hands down the best PC gamepad for your money would be this one right here. I've never been more satisfied with a controller for my PC and that includes using a 360 controller. It's got a switch on the back that lets you switch between xinput (360 controller) and direct input (old school gamepad for compatibility with older games.)
Also, have you ever played a side-scroller on your pc only to have it force you to use the joystick for movement because that's considered the primary directional input? That's what the mode button on the front of the logitech gamepad is for. It swaps the primary directional input between the gamepad and joystick for those kinds of situations. All around, it's a quality gamepad for the money and has versatility that you won't get from a 360 controller. It's good. Seriously.