3Delight Free - http://www.3delight.com/index.htm
Anim8or - http://www.anim8or.com/
Aqsis - http://www.aqsis.com/
Blender - http://www.blender3d.org/
Houdini (Free Edition) - http://www.sidefx.com/apprentice/index.html
Now3D - http://digilander.libero.it/giulios/Eng/homepage.htm
OpenFX - http://www.openfx.org
POV-Ray - http://www.povray.org/
SOFTIMAGE|XSI EXP - http://www.softimage.com/products/exp/v3/
Terragen - http://www.planetside.co.uk/terragen/
Toxic - http://www.toxicengine.org/
Wings 3D - http://www.wings3d.com/