This website was created by a father of a child on the spectrum, and it is extremely comprehensive. It explains ABA therapy in better detail and provides a wealth of info about it!
Website for Behavior Analysts Inc, a company that provides services and also has available for purchase assessment materials such as the ABLLS (James Partington's organization): http://www.behavioranalysts.com/
The Mariposa School, a VB School for children with autism, has a very comprehensive manual for parents who wish to attempt VB therapy on their own: http://www.mariposaschool.org/programs/