Instructables has a tutorial on a CD repair technique designed to bring nearly any disc (barring any cracks, breaks, etc...) back from the dead. The fix requires you to heat the underside of the CD over a gas burner, boil it in water and dry off your freshly resurfaced disc. The process seems to leave a slim margin of error, so if you're trying to recover something valuable, you better know what you're doing. [Instructables]
Had to try it tonight. Got some backups of my kids movies that are in very poor shape (and ones they won't miss). I had issues with where the fork touched the disc. It was extra hot there and would usually cause some sort of melting of the disc. I also found out that if you have a disc with lightscribe on it, that the lightscribe image will disappear. I wonder if you could just do the boil and then try to relightscribe it. That would be pretty cool. I tried one without the open flame and only with the boiling. It didn't have any warping issues and didn't do anything for the scratches. It looks like the open flame is what "heals" the scratches with the boiling just being a step to get it solid and back into shape. Most of these did get rid of most, not all, of the scratches, but I wouldn't ever try this on something that is important, unless you have no other options.