There are a TON of different options for software, so it's really a personal preference.
For me, I use DeltaCAD for most things, since I'm not a CAD guy. It's simple and easy, works well for parts and well enough for the artsy stuff. I am trying to learn Inkscape as time allows....it will do a lot better job at tracing images than what I've tried before, PlasmaTrace.
In any case, after the drawing exists, I import it into Sheetcam for processing, then to Mach3 for cutting.