Then try GeoGebra! This free site allows teachers and students to graphically represent geometry and algebra in ways that can then be manipulated by viewers. It is an amqazing tool to help students see basic geometric theorems and ideas as well as the algebra behind the concept. In addition, you can create dynamic number lines that demonstrate addition and subtraction. The tool is fairly quick to learn and easy to use in the classroom.
Dr. Vikki Costa conducted a webinar in August, 2011 that included an introduction to the tool, demonstration of how to create a variety of dynamic worksheets and applets, and ideas for using the tool in the classroom.