+2 on Sketchup.
It has a very forgiving learning curve, even for "specially challenged" individuals such as myself. I've been playing around with the Architecture layout and it's pretty good for making basic forms. Curves and circles are a bit challenging
Some tips:
1)Use the square tool for almost everything at first.
Using the measuring tape tool first is a safe way to add boundrys.
If you can't get them to connect(for some reason Sketchup seems to switch axises and/or purposely ignore the reference points), bring it close, and then connect it.
In the long run, its faster to work slower and hover over points to recognize them.
2)Do the simple layout first, double check measurments, then add details.
Much easier that way. Trying later-on to highlight a feature, make a component, and then move it usually ends up with the rest of model being pulled into a horiffic Picassoisque-result. Highlighting something picks up even the invisible lines all the way through the model.
3)Keep clean religeously, and switch to the view tool for viewing.
Erase extra construction reference points and lines to make the model simple and complete(switch to wireframe and then double-check the model didn't get in shaded).
If, for example, you spastically use the point tool while spinning the model, you will create hundreds of reference points which the corners of your boxes will jump to. After spending hours building off those boxes, you will then realize to your dismay that the original boxes are
not square and you will have to erase everything and start over
.