SIK Imp iPod AUX adaptor / charger
Connects your iPod to the AUX input of your car stereo via the dock connector on one end and a 3.5mm stereo jack on the other. This takes a constant level line-out signal from the iPod which is much better for feeding into a car stereo than the output from the headphone socket.
Also on the other end of the cable is a firewire connector which allows charging of the iPod via a cigarette lighter adaptor. Not 100% sure if there are any iPods that it won't charge. Used with an iPod Mini and a Nano (3G) which both charged fine.
See full details and spec here:http://www.sik.com/imp.php