Reddit mentions of Project Origami: Activities for Exploring Mathematics

http://www.mathman.biz/

http://wheelof.com/whitney/index.php?var=v1

http://vihart.com/

http://www.go.kestrel.nu/

http://www.amazon.com/Escher%C2%AE-Pop-Ups-Courtney-Watson-McCarthy/dp/0500515905

http://www.amazon.com/Alexs-Adventures-Numberland-Alex-Bellos/dp/1408809591

http://www.amazon.co.uk/You-Can-Cube-Patrick-Bossert/dp/0141326506

http://www.amazon.co.uk/Godel-Escher-Bach-Eternal-Golden/dp/0465026567

http://www.amazon.com/Mathematics-Very-Short-Introduction-Introductions/dp/0192853619

http://www.amazon.com/Project-Origami-Activities-Exploring-Mathematics/dp/1568812582

http://www.amazon.com/Origami-Tessellations-Awe-inspiring-Geometric-Designs/dp/1568814518

http://www.amazon.com/Proofs-without-Words-Exercises-Classroom/dp/0883857006

Once I got started ....whew. good luck!

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.