I went through this recently. Here's what I found:
* Pencil and paper - works and is useful for quick sketches, but I care
a lot about proportions and it was hard for me to draw accurately
enough to choose proportions correctly. Of course, then there are the
* DeltaCAD - cheap, has a free trial, and includes a good tutorial in
the help. More accurate than pencil and paper, but is nearly as
difficult to make modifications to the drawing, which I do a lot as I
move stuff around. If you knew exactly what you were drawing ahead of
time, then it would be great, but who knows that?
* SketchUp - It was really difficult for me to place objects in the
right location. 2D is sufficient for me. Struck me as the kind of
tool that you could spend hours and hours drawing as opposed to being
in the shop.
* Visio - I have this for work and find that it is actually the
easiest. Very accurate, allows draw and drop of objects, and allows
you to connect lines, which stay connected as you move. Those are all
very useful as you modify the drawing a lot. You can get a free trial
from the Microsoft site. The standard version, which is all you need,
is about $200, which isn't the cheapest, but is the easiest for me.