For dirt and/or fingerprints, I just use a plain microfibre cloth - with a little spit for more stubborn grease! Always wipe in a direction perpendicular to the tracks, i.e. from the inside out, don't wipe around the disc.
Personally I don't think that sprays or solutions offer any significant beneifts, but maybe others will disagree.
Scratches, on the other hand, need a more specialist repair kit.