I've got a USB to Amiga adapter and just use real Amiga joysticks on the PC if I want authentic feel playing Amiga games and other emulators.
Although personally the best for any retro games is the X-Arcade dual stick controller. Great arcade feel, heavy, robust, and it give a new lease of life to Amiga games because it gives a much better level of accuracy than any Amiga or other home controller ever did.
A couple of you mentioned the Xbox 360 controller. I actually have one that I used with Vista because so many recent games directly support the 360 pad, and for action games like Racing it is perfect. I also disagree about the controls. I've found the wired 360 controls to be very nice. A good robust feel to the controller and buttons. The analogue sticks work well and the D-Pad is fine. Although I will say I do prefer Playstation D-Pads. I know some people just can't get on with Playstation controllers D-Pads, but I've always liked them. Personal taste I think depending on what you used before.