Mothers plastic polish is great and available at most automotive parts stores. It is quick and easy and only costs about 5 bucks for a lifetime supply.
Aloha! I second the Novus. They also sell these at your local plastic store like Tapp Plastics. (You can find these in the yellow pages, they make acrylic covers for memorabilia collectors, businesses, etc.) I bought mine at the Container Store in Chicago. It is easy to use. I believe you apply #1 on the deep scratches, and #2 on shallow ones, and then #3 to polish it off. Works great!