Novus Polish is the plastic cleaner / scratch remover of choice around here. It won't remove deep scratches and it takes some elbow grease, but it can refursh acyrlic that has taken some general abuse from normal wear and tear. They have three levels, the first is mostly a cleaner, and the level 3 product is for surfaces that have more wear. We keep it around to clean up projects we are working on, and for acyrlic desk and lectern surfaces.
I have also heard that the product works good on scratched dvd's and cd's - though honestly, my trick there is to use toothpaste!
And for those you want to try out the product, you can try a set of the 3 levels out in a kit sold by Amazon for about $15.