The following links are always nice to take a look at, and as an added benefit they have a direct or indirect link to Natural Dressage.
The Art of Natural Dressage movies! At this moment we have movies on Chase the Tiger, the lateral movements, basic exercises with the cordeo and a movie on the Haute Ecole work. With Blacky in the courbette!
The Art of Natural Dressage forum naturally should be on this list as well: just read along or become a member and write with other Natural Dressage trainers!
My old Dutch website, completely devoted to training tricks with the clicker. If you're able to read Dutch, you'll find a lot of texts that are also part of the book that I wrote on trick training: Vrijheidsdressuur.
The website and international webshop of Josepha Guillaume, co-founder of the AND forum. She has some wonderful baroque cordeo's in her collection!
A huge webshop with regular Natural Horsemanship tools, but also with very unique, light leadropes that are wonderful for working with the cordeo.