I picked up the Taotronics TT-BA08 among others for the following reasons:
- Up to 20 hours play time. Others are less than 10 hours, cannot serve a whole day.
- Very small and light at 1 oz, ideal to clip on headphones as showing in above video.
- Full control buttons for play/pause and volume/track.
- APT-X for CD quality audio.
- APT-X low latency (short delay). You can use two of these, one as transmitter and one as receiver, to watch TV with any of your favorite headphones.
- Playing while charging.
- Connect to two devices at the same time.
If your headphones have high impedance such as the Sennheiser HD600, you may give Creative Labs Sound Blaster E3 a try, supposed to drive 500 ohms.
If you want one that comes with a clip on it already and for free, Fry's is selling a smartbean adapter, free after $15 rebate. Note that it does not have all the above features, but you have nothing to lose.