I just downloaded Autodesk 123D. I had high hopes and so far Autodesk has not let me down.
Sketchup was a great start in the area of simple 3D development, but 123D really steps up to the next level.
It's actually 4 little apps: Design, Catch, Sculpt, and Make
Check it out and tell me what you think. http://www.123dapp.com/