WARNING: this project involves the use and modification of laser devices. While the lasers I suggest using (store-bought red pointers) are relatively safe to handle, NEVER LOOK DIRECTLY INTO A LASER BEAM, BEWARE OF REFLECTIONS, and be EXTREMELY CAREFUL when MODIFYING a laser product. Also, I am not liable for anything stupid you do.
Here is yet another thing to do with those promotional laser pointers: send music (or data) from point A to point B over the laser beam using amplitude modulation. All it takes is pointing the moded laser at a detector, and music can be heard from an attached amplifier. The range and quality (or data speed) can vary, but I have gotten a HALF MILE of range with excellent audio quality and around 300bps of throughput.
The image shown here is the transmitter and receiver working across my desk during a test.TO SEE HOW TO USE TWO LASERS TO TRANSMIT TWO MUSIC CHANNELS AND MIX THEM WITH A PAIR OF SUNGLASSES, check out the blog post here.
A video of the system working can be found here: http://video.google.com/videoplay?docid=6895048767032879458&hl=en
Much inspiration for this project came from http://sci-toys.com/scitoys/scitoys/light/light.html#laser_communicator