The wonderful Mr. Clean Magic Eraser (TM)
Cutting up a magic eraser into rectangular pads and using them with a little alcohol on your playfield can have some amazing results. This is used to remove ball swirls and other playfield markups that come from years of use.
Caution: Rub softly in circles. If you do it too hard, it will take the finish off. You may want to practice in an inconspicuous place first. Also don't allow the playfield to stay wet too long, even with alcohol.