We've written before about Blender, the powerful open source 3D modeling, graphics and animation application, currently out in a much improved new version. Blender is in fact so powerful that it's been used to create very professional looking full-length animated movies.
The web, and the Blender.org site both abound with Blender tutorials, and the free online book Blender Basics is a good place to start learning the application, but Free Software Magazine alerted me to what may be the best free way to master Blender of all: Tufts University's Blender 3D Design online class.