Seriously! Some automakers have upgrades that include iPod adapters, drivers to play music from their iPod by allowing the adjustment in their car stereo systems. There are other car manufacturers with devices and adapters that read and play music from your iPod, but you must use the actual iPod to make selections and changes.
In addition to car audio systems iDog is iPet, iPod covers, (connect speakers and docking stations that the iPod to play without headphones connected) iPod player, iPod alarm clock and iBaby my favorite is (a pram by Kolcraft made that an iPod, speakers, and has built-in adapter, so that the baby is your favorite listening while walking in the city) or iCrib the device (iPod more designed brilliantly to keep the baby pacified-hopefully this nifty gadgets are evidence of saliva).
If you are on the market for a car sound system, then it is likely that this is already an iPod or not engaged seriously with the idea of having an opposition. If one or both are in the near future, I recommend buying a car sound system is fully compatible to use with your iPod or other MP3 players and other information you provide. But I think you are more options with the iPod in mind that other brands have not (yet) nearly the base of the buyer and the purchasing power of iPod owners are determined.