Architectural/Product imaging/animation/prototyping

Links

A list of low cost or free Software:

http://moi3d.com/

http://www.blender.org/

http://www.punchcad.com/

http://www.gimp.org/

http://www.inkscape.org/en/

A couple of rendering engines :

http://www.chaosgroup.com/en/2/index.html

http://www.maxwellrender.com/