I had a classmate in dental school who got a whole box of karaoke disks that were scratched beyond use. He used a benchtop lathe with a buffing wheel to polish them, first with tripoli, then with a product called hi-shine. They are used for polishing acrylic retainers. It took a while, but he got about 100 of them back in working order.
I have the equipment in my office but haven't needed to do the same trick. My wife bought the manual disk doctor which is a piece of crap in my opinion.
I should see how hard it is to do one in my office and start charging my patients to fix their games and dvd's