Aukey Portable Bluetooth 4.0 Audio Receiver car kit
The Aukey Portable Bluetooth Receiver comes with more features than many similar products and a clever means of remotely controlling playback from your phone, but it will involve running wires to a power outlet and an auxiliary input in a car.
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Pioneer AppRadio SPH-DA100
For iPhone 4 and 4S lovers, the Pioneer AppRadio 2 is possibly the best aftermarket receiver that money can buy. For Android users, the choice isn't so obvious.
Parrot CK3100 Advanced Car Kit
The Parrot CK3100 combines a simple, easy to use control interface with a good voice-recognition system to provide drivers with easy hands-free calling on the road.