RetroZone perfects the emulation experience

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.