Supplements for

Experiencing Geometry in Euclidean, Spherical, and Hyperbolic Spaces, Second Edition, 2001

with writing input from

Saads, Silvia, and Gary Davis, VISUAL PERCEPTION AND IMAGE FORMATION IN THREE DIMENSIONAL GEOMETRY. A study with pre-service secondary teachers.

University of Modena, Italy A "theater of machines" complete with pictures, animations, and mathematical proofs related to the large collection of geometric devices in the Laboratorio di Macchine Mathematiche. The text is Italian but the pictures and animations are exquisite geometry.

Cut-The-Knot . Interactive Mathematical Miscellany and Puzzles
Geometry Center at University of Minnesota
Geometry in Action. This page collects various areas in which ideas from discrete and computational geometry (meaning mainly low-dimensional Euclidean geometry) meet some real world applications.
Mathematics Forum . The Math Forum is a leading center for mathematics and mathematics education on the Internet. Formerly the Swarthmore Mathematics Forum, but now at Drexel.

The MacTutor History of Mathematics archive, a large, complete, and accurate website devoted to the history of mathematics. University of Saint Andrews in Scotland.

MathSearch from the School of Mathematics and Statistics, University of Sydney.
"Mathematics Resources on the Internet" mathematics links compiled by Bruno Kevius