3m is good stuff and many of the headlight restorers do work well. If they are not too shot some elbow grease and simple Cleaner/Wax can work wonders too.
I've used Meguiar's Plast-X, and it does work. I've only used it by hand though, not with a polishing ball (e.g. Mother's Powerball). Use a terry cloth for more "bite" when polishing, and tape off the painted areas adjacent to the headlight with blue painter's tape.