Reddit mentions of Origami Design Secrets: Mathematical Methods for an Ancient Art

Erik Demaine, Robert Lang and Tom Hull have great ones. Also check out the OSME conference proceedings. These people are always happy to talk via email if you have any questions, but you will have to look them up.

• Origami Design Secrets by Robert Lang
  
• Project Origami by Tom Hull
  
• Geometric Folding Algorithms by Erik Demaine
  
• 4OSME Proceedings
  
• 3OSME Proceedings
  
  Also I heard this one is good but I haven't seen it yet: Origamics: Mathematical Explorations through Paperfolding by Kazuo Haga, who I believe was one of the first to write academically about origami.

I just bought one of his books, in fact. Origami Design Secrets is basically the practical Origami theory book out there; it includes the optimization algorithms he uses to design bases, as well as several folding sequences for shaping flaps in bases into whatever you need. And a bunch of neat designs, like an intricately detailed Cuckoo clock folded from an uncut 10:1 rectangle of paper.

I think you're joking, but let me answer seriously. There are not diagrams for most advanced original origami nor will there be. Diagrams only exist up to a certain expert level (and there are more than enough of those) and beyond that point more complex designs are created and folded by advanced origami artists.

These folders are generally too busy with and interested in making new cool designs to go through the very different and extremely time consuming and laborious process of diagramming their work. :(

In fact, I would guess that someone who is a very good origami designer and a good diagrammer is a much greater rarity than someone who is one or the other. They are different skill sets.

At most you can find fold patterns sometimes (like the one in the photo referenced in another link in this thread), or a photo of an unfolded basic pattern. If you are experienced enough you can figure it out from the fold pattern.

I believe this was folded dry and then wet and shaped. The scale pattern was folded onto the appropriate areas of the paper before principal folding began.

Most of the techniques for designing a dragon like this (scales, claws, head) are provided in the book Origami Design Secrets: Mathematical Methods for an Ancient Art http://www.amazon.com/Origami-Design-Secrets-Mathematical-Methods/dp/1568811942/

I've folded a lot of nice dragons that are not nearly this complicated. I'll tell you what would be the biggest pain is folding all the scales. The rest of it would of course be insanely complex as well, I don't think I'd attempt something like that myself.

Edit: Here's a picture of a much simpler chinese-style dragon design with diagrams available in a popular origami book that you should be able to get a hold of by John Montroll: http://www.giladorigami.com/File.php?File=P_DragonC_Montroll.JPG

Once you fold this body, you can lightly wet it and curve it and round the body out to make it look cooler. The book is "Mythological Creatures and the Chinese Zodiac in Origami" by John Montroll