SketchUp

SketchUp is a 3D modeling software for Windows and Mac.  I have modeled our house we are building in Bloomington, IN, with SketchUp, and I have gotten deep enough into it to conclude that it is really a strong professional tool for design and presentation graphics.  SketchUp is free, with a professional package offered at a very reasonable price, but I just use the free version at the moment.  There is also an energy modeling plug in, as well as solar site analysis when you integrate with Google Earth.