I found this a while back and figured it'd be useful to post here. it's a generic I/O connector for the iPod that you can solder up to whatever you want...
$4 too makes it quite reasonable...
alternative source here: http://home.swipnet.se/ridax/connector.htm
and just for good measure here is a pinout for the connector:
and of course it wouldn't be complete without the Apple Accessory Protocol; how to communicate with the port:
ok now I expect all of you to start making your own iPod accessories