Auto Glym - Glass Polish works a treat
or you could use wax and grease remover (or prepsol) with a razor blade that will clean the surface prior to polishing
Best polish i ever used was Fercela G3 it could get out any scratch in one small application
Megquires - Wet Look also works heap's well
Auto Glym - Super Resin Polish (the red and white bottle)
Omicron - Premium Wax