More often than not FM transmitters that pump tunes from your MP3 player to your car’s radio are junk. The local radio stations interfere and if you’re antenna resides at the rear of the vehicle then may God help you.
Technical hurdles aside, New Potato Technologies TuneLink Auto device is looking pretty snazzy. Instead of having to jack the FM transmitter into your iPod (or iPhone or iPad) you connect the two over Bluetooth. The dongle/cigarette adatper then beams the music via FM transmission to the car’s radio. If Bluetooth doesn’t meet your fancy then you can jack directly into the FM transmitter using the 3.5mm headphone jack and charge your iProduct by way of the USB port.