If computer methods don't help, i use last one, but usually effective method - polish. Nothing very special required. I have successfully used even car's color restorer liquid. For deep scratches manual polishing can take long time. In this case i used electric polish (orbital sander). But it requires to be careful.
Of course, it help only for scratches in plastic (bottom) side of CD. No way to restore CD with damaged data carrying (upper) layer.
Results may be not so god for CD-R, CD-RW or DVD. Possible because of polishing plastic layer transparency is going little reduced.
Note: before use this methode for valuable CD, try on something worthless!
