Advances in computer graphics have provided mathematicians with the ability to create stunning visualizations, both to gain insight and to help demonstrate the beauty of mathematics to others. As educators these tools can be particularly important as we search for ways to work with students raised with constant visual stimulation, from video games to MTV. Computer generated images, animations and interactive demonstrations permeate all areas of mathematics education, making it important for educators and researchers to determine how best to harness these tools to increase student learning. This survey article discusses what we know, and do not know, about creating effective visualizations and describes possible avenues for future work in the area.