Navigation/GPS car mount options with FM transmitter

I've been looking at the different iPhone mounting options. I am interested in the GPS enhancing units, such as Tom Tom or the yet to be released Magellan car kit. In my research, it seems that the Tom Tom car kit comes with a line out for playback of audio. Unfortunately my car is not equipped with an aux jack and I must transmit the audio to my car stereo via an FM transmitter. Does anyone know of a GPS enhancing car kit that gives includes an FM transmitter for playback over the car stereo? I can't give up my tunes in order to use Navigon.