I've just been checking out Google's free version of SketchUp and I like what I see. It was quick to get going and there are some features that make creating three dimensional images easy and fast. Something that I will need to give more attention to though, is the fact that SketchUp offers an API using the Ruby programming language. This allows third party developers to add functionality to the package. It's kind of like Script-Fu in the Gimp, a highly-recommended, open source 2D image editing package.