Furniture polish is supposed to be good because it "fills in" the scratches and is non-abrasive. I've used it and it certainly does not make things worse. Choose a non-coloured or light-coloured type. If you use a spray polish, test it on a waste CD first, in case the solvent in the aerosol damages the surface. (It didn't when I used it).
I've heard anything from a banana peel, plain white toothpaste to rubbing compound will help get rid of scratches on a CD. I don't know if any of those things work. I guess you'd have to try one and see...