Geometry

The Pythagorean Theorem Lesson - A lesson on the pythagorean theorem with the objective that the you will discover for yourself the actual theorem.
http://www.arcytech.org/java/pythagoras/index.html

Point Out the View - Use visualization to determine how four different people see a set of 3-D blocks. From PBS Kids.
http://pbskids.org/cyberchase/games/pointofview/pointofview.html

Tangrams - Choose a puzzle, then click and drag virtual tangram pieces to solve it. From PBS.
http://pbskids.org/sagwa/games/tangrams/index.html

Brain Teasers: Geometry Puzzles - Slice and complete various figures to form requested shapes.
http://brainden.com/geometry-puzzles.htm

Fugues of the Well-Tempered Clavier - Interactive Director movie comparing a fugue by Johann Sebastian Bach to a Möbius strip.
http://jan.ucc.nau.edu/~tas3/wtc/i10.html

Teen Math Whizzes Go Euclid One Better - Features a discussion about the works of two teenagers, David Goldenheim and Daniel Litchfieldm, from Connecticut. They helped find a solution that eluded Euclid in finding a method to partition a line into any number of equal sections.
http://jwilson.coe.uga.edu/Texts.Folder/GLaD/GLaD.Comments.html

Introduction to the Works of Euclid - Covers the life of Euclid and a discussion of Euclidean geometry.
http://www.obkb.com/dcljr/euclid.html

Mad Maths - Contains proposed mathematical theorems in a fun way.
http://www.freewebs.com/maths88/

Spaceship Builder - Use a virtual geoboard to help Dr. Marbles design a new fleet of cyberspace ships. From PBS Kids.
http://pbskids.org/cyberchase/games/perimeterarea/perimeterarea.html

Geometry from the Land of the Incas - Presents problems involving circles and triangles, with proofs, SAT practice quizzes and famous quotes. Also, has examples of geometry in Peruvian culture.
http://agutie.homestead.com/

Spaghetti and Meatballs For All - Webquest for 3rd-8th graders comparing the perimeter and area of rectangles. Relates to the book "Spaghetti and Meatballs For All!" by Marilyn Burns.
http://www.viterbo.edu/academic/ug/education/edu250/kljohnson/

Figures and Polygons - Shows different types of straight-sided shapes with up to ten sides. Gives the total number of degrees for each side.
http://www.mathleague.com/help/geometry/polygons.htm

Areas, Volumes, Surface Areas - Use these simple illustrated formulas to calculate volume and surface area of various shapes.
http://math2.org/math/geometry/areasvols.htm

Geometria - A program for computing lines, surfaces and volumes of the main plane and solid figures, through direct and indirect formulas. Includes multiple languages.
http://www.elvenkids.com/tools/geometria/Geometria.php

Tim's Triangular Page - Learn about the basic properties, formulas, theorems and different types of triangles. Includes proofs and illustrations.
http://sakharov.net/triangle.html

The Everlasting Pi - The history, uses,and creator of pi and also some fun facts, jokes and songs.
http://www.freewebs.com/abishek/

Geometry - Explains and describes geometric terms, measurement of angles, types of figures, coordinate graphs, areas and volumes.
http://www.mathleague.com/help/geometry/geometry.htm

Cynthia Lanius' Lessons: Geometry Online - Have fun learning through activities about polygons, triangles, circles, and the volume of cylinders. Page includes an historic timeline, SAT type quiz, and glossary of terms.
http://math.rice.edu/~lanius/Geom/

Geometry - Games, illustrations, and definitions.
http://www.coolmath4kids.com/geometrystuff.html