I'm sure this is well documented somewhere, but I figured it out myself, so I thought I'd share.
I was playing my Atari 2600 in the back room at work, and it occurred to me that its stock joysticks were perfect. I'm sure it has something to do with having been 8 years old in 1979...
Anyway I took it apart to see what it was. It's just 5 switches (up, dn, lt, rt, fire) and a common ground, which was very familiar to me from having built my control panel around an IPAC.
So I found the pinout for the connector here:
http://www.computerrepairservice.com/cables/co_JoystickAtari2600.htmlwent to Radio Shack and got the crimp-together "9 pin D-sub male" jack that the connector mates with and in about 10 minutes had an Atari 2600 Joystick port (via the IPAC) on my cocktail cabinet.
It allows me to play joystick-and-one-button horizontal games from the sides of my cabinet where there are no built in controls. Bosconian is a blast with it.
Radio Shack only had one jack on its rack, so I'll have to go back (I'm a poet) to get the player 2 port later.