Here are some links to resources I found useful. Plus links to the Parelli Principles and the Equitation Science Principles for comparison.
If you have any other useful sites please contact me and I will consider them for addition.
This is new site for all aspects of positive reinforcement training.
Some tips on using positve re-inforcement when riding – Shawna Karrasch
Some regional resources
Sussex based Ride With Your Mind coach Sally Ede
Glossary of terms from the Association of Animal behaviour Professionals.