For your headlights, if they are like mine were, you can get them like new with a plastic polish, such as Meguiar's PlastX. It's like a creme, but it contains a very mild abrasive. It works like a charm, and it really makes a difference.
You could also use sandpaper with very fine grit, like 1500-2000 (used with water), and finish it with jeweler's rouge, like mentioned in the other threads mentioned above..
