Blender – 3D Modeling, Rendering, Animation, Video
Blender is the free open source 3D content creation suite, available for all major operating systems under the GNU General Public License. Its interface is tough to learn at first. But, after some hours with video tutorial instruction or books it becomes a very valuable asset to your personal production pipeline.

Daz Studio – 3D Figure Poser
Daz Studio is a very powerful 3D figure poser, and the best part about it is that it’s free. You can pose, light, and animate your figures in 3D space. Then, you can render detailed images or video right on your desktop computer. Daz also offers a variety of downloadable 3D models and other content in their store.

Google Sketchup – Simple, Powerful 3D Design
SketchUp is one of the simplest 3D programs to learn, and Google offers a free version! It is perfect for doing simple architectural renderings and layouts. Even the kids will love this one because of its ease of use. The free version can render architectural style sketches, and is very cool.