Free 3D program
There is no doubt that Blender 3D is the most popular opensource and free 3D program in the world. We have some Blender tutorials on this site, such as Blender transparency map and Realistic rendering using Blender 3D.
However, it is not the only one. There are other pretty good but free 3D applications as well.
One such free program is Art Of Illusion. This program is somewhat easier to use that Blender 3D. However, it cannot run off the download. You will need Java virtual machine in order to run the program.
To go to Art of Illusions website, click here.