USB Classic Joystick
Over at ThinkGeek you can get ahold of a classic Atari joystick with a modern USB connector. It works with console and arcade emulators including Stella, VICE and MAME and is compatible both with Mac and PC (no drivers needed). More info inside.
It also works as a standard USB joystick. You can buy either one joystick for $24.99 or a 2-pack for $39.99.
USB classic Joystick [thinkgeek.com]