Autodesk, make of AutoCAD and other CAD and design software titles, is now offering AutoCAD and Fusion 360 free for education use. Students can use it at home and at school, giving them and teachers new tools for them to use in some great projects.
The education page, http://www.autodesk.com/education/home, has the download links, as well as resources, training tips, help and support, and more.
My Top 10 Free Google Resources for Education - includes Google Sketchup 3D modeling software.
NASA 3D Resources - fun and educational - includes downloadable models to use in CAD.