Some interesting info on diet. We have had much success with the GF/CF/SF (Gluten Free/Casein Free/Soy Free) Diet with our son, as well as many of the supplements which are recommended for kids with ASD. Much of it is trial and error as each person is different and reacts differently. But from our experience and many other parents we know, talked to and read about, they have had very similar experiences.
Here are some great books/links to help get you started!