Ipod
Lots of ways to go... Easiest is the FM kit made by some folks. It transmits the IPOD audio via FM and you dial it up on the radio. ALso has a convenient cradle and bracket for mounting the ipod.
Other way is the old faithfull cassette adpator. The one with the cable coming out to plug into the headphone jack. There is also a way to wire it inline with the CD changer, but you need to know what you're doing or you will seriously foul up the CD changer and if you hit the 12V lead, your IPOD.