^ I would say google sketchup
You're not going to get professional grade renders or high poly models out of it, but that is not the point. I use sketchup all the time, and it has a relatively easy learning curve (
www.google.com/sketchup)
All of the Edmonton 3d buildings featured in Google Earth have been done by Newfangled. Working with Google Earth and Sketchup is awesome.
With sketchup you can also get professional rendering software that renders your models so they are at least presentable... Ill provide some examples in a sec