I just got a Sennheiser BD 300 Audio Bluetooth/headphone jack transmitter. It's a dongle, about the size of pack of gum, that plugs into a standard 1/8" stereo jack. It transmits the signal from there to a Bluetooth device, such as wireless headphones.
The lithium-polymer battery is charged via a mini-USB port on one end of the dongle; it takes about 3 hours to charge from completely discharged, and supposedly will run for up to 14 hours on a charge. The other end of the dongle has an integrated 4" audio wire, terminated in a gold 1/8" stereo plug.
Once the battery is charged, the dongle can be disconnected from the USB cable, and and plugged into any audio headphone jack, making it very useful for portable SW listening. I am using it to transmit the audio from my Sony 7600GR to a pair of Motorola S305 headphones; it works very well, and is particularly convenient, since all three devices are battery powered.
The best price I could find was $76 dollars, with free shipping, from B&H Photo.