I must admit I have very little knowledge about CAD tools but even so, I found this application quite easy to use.
gCAD3D is a computer-assisted design application that enables you to create and render three-dimensional models without having to spend half your income in an expensive designing tool.
The program looks easy to use and includes complete documentation, though not updated to the latest version. There are also a bunch of pre-rendered 3D models which you can use to get you started or even import them in your own projects. gCAD3D features a quite plain interface, focusing mainly on the working area and putting the emphasis on information and usability.
In all, gCAD3D looks like a great 3D design app to start with, but maybe a bit too plain and simple for more advanced users.