From Trimble Navigation:
Google SketchUp is a free, easy-to-learn 3D-modeling program with a few simple tools to let you create 3D models of houses, sheds, decks, home additions, woodworking projects, and even space ships. You can add details, textures, and glass to your models, and design with dimensional accuracy. You can place your finished models in Google Earth, share them with others by posting them to the 3D Warehouse, or print hard copies. Google SketchUp is a great way to discover if 3D modeling is right for you.