Following their recent trend of getting their grubby little mitts into EVERYTHING, Google, now offers a simplified 3D app, called SketchUp.
I just came across it, myself, and thought some people here would like to know about it.
The download page is here -
http://sketchup.google.com/download.html
For a review and screenshot, click here -
http://bothack.wordpress.com/tag/graphics/
I'm going to give it a try, myself, and may post my thoughts on it, later.
EDIT: After downloading, at that first link, you're able to watch several tutorial videos which show how simple this program can be and what you can actually do with it. They are, definitely, worth watching, should you decide to try it.