Comment Pinouts.ru (Score 1) 262
Check out the Videogame Connector Pinouts at Pinouts.ru. Many of them include suggestions for connecting them directly to a PC.
You could also get something like the Ultimarc U-HID or I-PAC. Many MAME users have been using these for years to adapt the controls in their arcade cabinets to work with PCs. You'll have to wire up a connector to let you plug in whatever kind of joystick you want but the flexibility means you can use it with several different controller types.