Google SketchUp is a great program for students to explore concepts in 3D geometry. We will be using it in class, but if students want to get their own program for use at home, it is free to download and use.
More information about Google SketchUp can be found here:
Google SketchUp for the Classroom
You can download Google Sketchup 8 directl from here:
http://www.sketchup.com/download
You can find tutorials to get familiar with the program here:
http://www.sketchup.com/learn/videos?playlist=58
