GeoGebra and GeoGebra Wiki are great resources for high school math teachers. GeoGebra is free software that math teachers can use to create visualizations of mathematics concepts. GeoGebra software can be used to generate worksheets and problems to accompany visualizations of mathematics concepts. GeoGebra Wiki has a good collection of resources and ideas from other teachers using GeoGebra software.

GeoGebra has recently released version 3.o which allows users to customize their tool bar. The newest version of GeoGebra responds to key board commands or drag and drop commands using a mouse.

Applications for Education
GeoGebra is designed for use with high school level math curriculum. GeoGebra incorporates Algebra, Calculus, and Geometry. Teachers can use GeoGebra to develop activities to use with students. I can also envision having students use the software to develop their own visualizations of mathematics concepts.

Below is an image from one visualization and activity that a teacher developed using GeoGebra.