NLVM Geometry: This site has everything you you would want to visualize with geometry. You are able to play around with different graphs and see what happens under different rotations and many other things.  It includes a few different types of GeoBoards. (contributed by Beth Postema, MCC Student, Winter 2007)

Animated Proof of the Pythagorean Theorem: A nice animation of a geometrical proof of the Pythagorean Theorem. (contributed by Carole Sutphen, Math on the Web Participant, MCC, Winter 2007)

Area Explorer (Interactivate): This one shows the student a graph of connected, shaded squares, and asks the student to find the area and perimeter.