Geometry

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

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

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

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

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

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

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

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

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/

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

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

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

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/

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

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