Here are links to a few more open source render engines and the free Panda3d modeler.

http://www.kerkythea.net/joomla/

http://www.luxrender.net/

http://www.indigorenderer.com/joomla/

http://sunflow.sourceforge.net/

http://www.panda3d.org/

Kerkythea has a built in importer for .skp files for native import of Google SketchUp scenes and there is a Blender to .xml script for use as an external render for Blender. It supports import of the usual model formats also. A very nice application, I highly recommend it though it is a pain to work with Poser/DAZ figures because of the way the material zones are setup on the models.

Luxrender, Indigo, and Sunflow are all good physically based render engines.

Panda3d is a free modeler by Disney and maintained by Carnegie Mellon University that covers modeling, rendering, and game dev.

Almost forgot about Art of Illusion, another open source modeling and rendering application.

http://www.artofillusion.org/