Geometry Junkyard: Origami: Resource listing of links for information about the relationship between origami and geometry.
Helena's Origami: Modular origami and tessellations by Dr. Helena A. Verrill. Instructions included.
Jim Plank's Origami: Modular: Diagrams and gallery of many geometric models.
Krystyna Burczyk's Origami: Photos of regular polyhedra models.
Mathematical Origami: Origami models and techniques with strong mathematical precepts.
Meenakshi's Modular Mania: Image Galleries of original modular models as well as picture links to other designs.
Modular Origami: Instructions, diagrams and pictures of various modular models in English, German, and Russian.
Modular Origami: Images of modular origami models folded by Michał Kosmulski. Model categories include: fractals and IFS, interesting mathematical objects, polyhedra and balls, spiked balls and stars.
nuwen.net - Origami Polyhedra: Illustrated directions for making four types of polyhedra.
Origami Mathematics: Mathematics of paper folding; includes a bibliography of articles and journals, Combinatorial geometry syllabus, and a tutorial on geometric constructions. Photo gallery of completed modular, geometric, and tessellation models.
Origami Tessellations: Blog by Eric Gjerde featuring tessellations, crease patterns, tessellation geometry, origami mathematics and paper folding in general.
Teaching Mathematical Thinking Through Origami: Suggestions for using origami to teach concepts in mathematics, with diagrams of models.
Thoki Yenn's Cuboctahedron Folding Companion: Step-by-step photo instructions for Thoki Yenn's 3D cuboctahedron origami model.
Tom's Origami Gallery: Personal gallery of modular and tessellation models.