SketchUp
Google SketchUp is pretty amazing. A few two minute videos, and you've pretty much learnt how to use every tool in the program - enough to create some pretty impressive models.
And everything is very intuitive. For example, there's the system of 'inferences', which is basically a snap-to tool that shows you how the current point is constructed (like how you'd construct a point in 3rd form Graphics). So, hovering over the midpoint of a line, then moving the cursor in any axis direction lets you place a line along the axis, perpendicular to the midpoint of the first line. It makes more sense when you do it.
The first video tutorial I saw, and a good introduction to what SketchUp does, is here - it's a simple dog house.
