I use AutoCAD, but any drafting type software should be useful. I've actually been making a library of parts, controls, monitors, etc. all drawn in .dwg format, but it's one of those things that I only get a chance to work on in my free time... After I get it somewhat organized, I am going to make it freely available. I imagine that others like 1UP also have a nice library of solid models, but that's not my gig.

I typically make many different control panel layouts and print them out full size (during lunch hour, of course!) on our large plotters at work. Here's a snap of just a couple of monitors and the Happ 3" trackball, along with a couple of control panel layouts for my last cabinet.
http://www.oscarcontrols.com/tmp/controls.gif