This is a topic I am also particularly interested, but don't have much to add. One that comes to mind is Google Sketchup, but not sure if it is appropriate (never used). What about Autodesk Inventors (not sure the cost)?
How do you usually go about manufacturing your own devices, parts, etc from the AutoCAD designs you create? Do you send the drawing to something like ponoko.com or shapeways.com or something more professional like redeyeondemand.com?
I am even considering something like reprap.org but my biggest problem is learning how to design joints, choose the right materials, etc.