http://www.densionusa.com/main.htmHooked my wife's car up with this. Little bit of a headache at first, but now that it's up and running, it rocks. Connects direcly to your stereo (in place of you CD player). It comes with it's own software, which will allow you to move through your iPod with your stereo controls, or you can bypass it and just use the iPod interface. Comes with a cradle that attaches to your dash.
Sound quality is amazing, I'm looking to put one in my car as well. The setup is pretty pricey though, but overall I'd say it's worth it.