Please contact me to recommend additions or deletions, or to let me know that a link is dead. (Last update: 2.1.11.)
Geometry: The Supplement - a young teacher's alternate version of geometry with handouts, slides, and material. Indeed a good supplement.
Khan Academy - a vast collection of YouTube video clips to illustrate many geometric matters.
Math Open Reference - what it says; this is the geometry page.
Purple Math - algebra review for all levels.
The Elements - an outstanding site that has the complete text with interactive diagrams and full supporting notes.
Byrne - an interesting presentation of Euclid soley in terms of colored shapes (if words and concepts are too abstract for you).
Art - a Dartmouth college course page about geometry in art and architecture. Well illustrated.
Fibonnaci - an extensive site about the series.
Golden Section - related site about the golden section.
Geometric Mean - an interactive site on the topic.
History - the geometric mean in history and architecture.
Solids - an introduction to the Platonic Solids and their use.
Interactive - a site that allows you to manipulate the various solids.
Investigation - questions (and answers) to help understand the properties of the Platonic Solids.
HRW - the textbook site for Platonic Solids.
Blueprints - cut out patterns for making Platonic Solids. This is part of a much larger site. Here is the section on geometry!
Simmons - Bruce Simmons' (former SSES math teacher) helpful illustrated dictionary of math words and concepts.
Patterns - a site devoted to patterns of problem solving. Useful for those who find proofs perplexing and mathematical reason odd and obscure.
Rutkowski - a full site devoted to the St. Stephen's geometry course materials.
Trigonometry - an excellent interactive site for trigonometric functions.
Calculators - a site offering calculators for every sort of topic you can imagine.
Factoring - understanding factoring through geometry
Doodling - a series of doodling videos by Vi Hart.
Math Fun - a fun and games math help site.
Fun Facts - more math fun and games.
Math Cats - another fun site.
Sketch Up - a Google tool for 3D modeling (drawing three-dimensional objects).
Geogebra - a sophisticated software for a variety of mathematics (geometry, algebra, calculus). Best if you look at the site to figure out what it is.
Giffy - can be used for making diagrams.
Web Resources for Math Teaching
Gooru - teaching and learning resources for teachers.
TI - webinars for TI calculators.