Docooler® Streambot Y Wireless Bluetooth FM Transmitter Radio Adapter Handsfree Car Kit with Hands-Free Calling, Music Control, and Charging Port for iPhone 5S 5 5C 4S 4 iPod, Android cell phone, MP3 Players and other devices
I have used several FM transmitters, and this one is by far the best one I have used.  It does take trying a few different stations to find the one it locks on to the best.  The hands free calling function does not work very well, but that's not what I bought it for.