Geometry

Geometry Manipulatives
The National Library of Virtual Manipulatives

Schmoop Geometry
Learn about the inner workings of isosceles triangles, what makes trapezoids tick, and why shapes are so special.

Homework Help - Geometry

Geometry Help 
A variety of help topics are available 

Java Sketchpad 
Dynamic Geometry for the Internet. Check out their demo gallery, the sine waver is a really cool demo of the construction of a sine wave.

Polygon Playground
Arrange designs with online movable polygons - hundreds of polygons to drag anywhere you want. 

Algebra and Geometry 
Presentations, worked examples and simulations on Algebra and Geometry.