Quick & Easy Laser Show Unit        

For a scanning system, purchase a "laser widow" unit ( they have an internal microphone that reacts to music, creating synchronized beam patterns in the air) from ebay for approx $50, and spend another $10 or so on a metal case.  Than all that's left is for you to spend an hour or two with a screw driver and a potentially a drill, and voila! you have a professional lasershow at a bargain basement price!
Prototype example - quick and dirty assembly (had a show asap 8)

To see some great pictures of the possible output (will depend on your scanning system), please visit our friends at absee-laser.