SketchUp is a 3D modeling program designed for professional architects, civil engineers, filmmakers, game developers, and related professions, recently acquired by Google. Developed by @Last Software from Boulder, Colorado, it is marketed as an easy-to-use conceptual tool with a simple graphical interface.
Render Plus offers several add on Products for Sketchup - including IRender nXt
Google SketchUp (free) is the free version of SketchUp.
SketchUp Pro is the full version of SketchUp.
Both versions of SketchUp 6 are approved for bot commercial and non-commercial use.
For more on SketchUp - see the SuWiki article: