Over at the RetroZone they've taken a slew of classic console controllers and converted
them to USB for use on your PC. The site features NES (including the Advantage), SNES, Genesis, Atari
Commodore, and Intellivision controllers/adaptors. There's also a kit you can buy to build your own
"RetroPad". The prices are fairly reasonable, especially since the rest of the emulation technology is
free.
Engadget
TUAW