[notice]NEVER look into a laser that is capable of engraving materials – you could be instantly blinded!  If you actually have to be told that, then you probably shouldn’t be allowed to use anything remotely dangerous.  DO NOT attempt to build anything like this unless you are willing to take full personal responsibility for any damages.  We WILL NOT be liable if you stupidly choose to build something like this and manage to damage your eyesight, or any other part of your body! And if you do choose to attempt to build something such as this, we strongly recommend mounting it inside an opaque protective enclosure, so that children or animals cannot come into the direct or reflected path of the laser beam.[/notice]

This looks like a fun but potentially VERY dangerous project – we wish the sites linked below had included some common-sense safety warnings for potential builders.  Please be conscious of friends and family members (especially the young ones) that might not fully appreciate the danger.  If there are drunk people around, hide this thing, preferably under lock and key!

I recently made a mini CNC laser engraver using two DVD drives salvaged from old computers and <$10 extra parts bought on eBay. The controller of the CNC machine is a Raspberry Pi, a $35 credit card size computer. The engraver turns out to be pretty successful. So I am sharing it with everyone.

Full article here:
A Raspberry Pi controlled mini CNC Laser engraver (fun of DIY)

Additional coverage:
Raspi Mini Laser Engraver (Hack A Day)
Raspberry Pi Laser Engraver Created Using Two Old DVD Drives (video) (Geeky Gadgets)
Home-made CNC laser engraver (Raspberry Pi – this article actually does include a warning!)