Use GeoGebra for Algebra Teaching

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. (Description from its official web site – link)

Here is a good example of how to use GeoGebra to teach algebra content: Car Race Problem http://mathcasts.org/gg/enliven/af/lines/slopes/car_race_anim.html