GeoGebra is free and multi-platform dynamic mathematics software for all levels of education that joins geometry, algebra, tables, graphing, statistics and calculus in one easy-to-use package. It has received several educational software awards in Europe and the USA.
This is a site that shows a software you can have at your school. It engages the 21st century learners. You do have to call them to get it for your school, but it looks like a great source.