London Drugs sells Griffin Brand ones, the charger and FM transmitter are together in one cord that plugs into the iPod connector, so it leaves the headphone jack free. Nice and clean, relatively inexpensive, ours works pretty good.
http://www.griffintechnology.com/products/itripauto
About 70 or 80 bucks I think. If you already have a charger, london drugs has just FM transmitters for fairly cheap too.