I run a Monster AirPlay FM Modulator. It works ok but could be better. You also lose some quality becase it's going through FM radio.
I've noticed many OEM cars now are going to have a AUX-In. I think this is because Satalite radio is really spreading. Before you'd be lucky to find a CD receiver with a AUX-in. There have been Cassette players with them though. Now, you can get decent CD Receivers with AUX for around $100. JVC, Clarion, Pioneer are jsut a few I've seen.