Daft as it sounds, I have successfully recovered both CD's and DVD's in the past by using metal polish on them. It was good enough to get a read off them to back them up.
I had a DVD disc that was particularly bad and had been scratched and scuffed to the point it wouldn't read at all. I used some fine grade automotive valve grinding paste on the surface until the scratches wasn't visible any more, after that I used some chrome polish to bring it to a mirror finish. Worked a treat long enough to get all the files off it!
