iPod car kit compatibility is as follows:-
Pioneer- any head unit with "P" in the part number is compatible (DEHP or KEHP) part (CD-IPB100)
Alpine- any head unit with "A" in the part number is compatible (CDA or TDA) part (KCA420i)
Kenwood- any head unit that is "Cd Changer" compatible from KDC4 and above, part (KCA-IP500)
Sony- any head unit that is "Cd Changer" compatible from CDXF and above, part (IPOD001)
Jvc- again any head unit "Cd Changer" compatible will work with iPod interface
Factory fit Gamma, Beta and Delta 6 are also compatible (MK4 & MK5)
General rule of thumb, any unit that can run a changer can run an iPod, the leads above are proper kits that charge and run the iPod through the head unit.
You can also do 3.5mm jack to 3.5mm jack (AUX IN) but it will not charge or control iPod.
Hope that helps