I second Lapierre's suggestion about getting a new head unit, unless you have changer controls in which case you can do the add-on devices which give you an auxiliary input. I've used several FM transmitters and the best I've used is the HK Drive+Play which has a really nice big display that you can mount on your dash which is similar to the Ipod menus. It is still FM-based, however, so an auxiliary input or USB input is going to give you a much higher quality sound.
