CAD is a sore spot on the Mac; none of the high-end (CATIA, I-deas, Pro/E, etc) or popular (AutoCAD, SolidWorks, etc) CAD packages are available. This is rather odd to me, since some of the packages run on Windows and a half dozen unix-like OSs, but not OS X.
There are a few Mac-only or Mac-focused CAD packages: ArchiCAD, Power CADD, VectorWorks