Ornamental Origami is a wonderful book for both math and origami lovers alike.
The author provides a basic description of common folding techniques as well as some other folding guidelines for beginners. A small section is also provided drawing the connection between modular origami and mathematics.
The models given in the book range in difficulty, but be warned: patience is a prerequisite for all of them. That being said, the author provides wonderful, clear descriptions and beautiful photographs.
Another interesting aspect of the book is the afterward: a small collection of mathematical exercises related to folding paper. The problems were thought-provoking and again bridged the gap between math and origami.