Google SketchUp is a completely free and easy-to-use 3D modelling
software. It doesn't compete against full-blown CAD tools or
professional 3D software, but has pretty much all the features a home
3D hobbyist can ask for. And yes, it is completely free for personal
use.
Software allows exporting finished projects to Google's 3D
Warehouse and can also place the SketchUp -created models on Google
Earth's maps. Obviously the projects can be also saved on HDD and
printed out.
http://sketchup.google.com/