Let's say you, um, found some way of playing old console games on your PC. You cold use a keyboard, or a 360 pad, but that's lacking in authenticity. No, if you're playing a classic console game, you need a classic console controller.
Think Geek are thus selling what they're calling "Classic Console USB Controllers", but which are really just exact replicas of everything from the Genesis pad to the GameCube controller. There's even an old Atari joystick.
I haven't used one, so I can't vouch for their build quality (it's just the shells that look identical), but being PC pads they all let you reconfigure the buttons, which is a nice touch.
They're $15-20, so hey, even if they're not the greatest controllers, they might be worth it just for appearance's sake. Not to mention muscle memory's sake.
Classic Console USB Controllers [Think Geek, via Gamefreaks]