Max from Zedomax made a cool Green Laser Light Show device and in true DIY style there is an abundance of parts that are available from your local hardware store.
"This simpler green laser projector was made so I could use it for my next party and I always wanted to make this. Although this laser projector only does one animation, 2 whirpools, I planned to improve upon after making this very basic version."
http://hackedgadgets.com/2008/05/09/diy-green-laser-light-show/