Someone else mentioned Meguars Plastix. That would work, I have some plastic polish made by Blue Magic I got at Autozone (I couldn't find the Meguiars stuff).
Also, you can use their metal polish (Blue Magic) for a more agressive cleaning (it's blue). I've used the metal polish to take out some pretty deep scratches in a watch I wear daily. I took it to the top of a mountain and it got a bit banged up on the rocks. Most of the scratches are non-existant now. I used it on my instument cluster on my dash and got rid of some annoying spider webbing effect from minute scratches.