For a bluetooth setup in your car, I've recommended Belkin's solution in the past. In fact, it's still the aux input method that I have, however, my aux input has recently stopped working. I've been using a portable bluetooth speaker as a stopgap, but still craved a way to play through my car's speakers without replacing the entire stereo.
Thankfully, Wirecutter reviewed bluetooth FM transmitters last week. For some unknown reason, I failed to think of this solution. At only $30 on Amazon, I snagged the top pick - GOgroove's FlexSMART X2 FM Transmitter.
The device offers all you need and provides a much better than expected sound quality over blank FM stations. Once installed, it'll automatically connect to your device when your car powers it, while offering player controls and an added USB port for charging.