If you can find the type of polishing pads that are used to remove fine scratches from glass (like a watch face) that would be the best - they are effectively very very fine sandpaper (4000 grit) and are used by jewelers. There are various cremes that are sold in record stores and places like Best Buy, but I don't know exactly what they contain.
DO NOT use something like 'Disc Doctor' that actually resurfaces the CD.