One major application still missing on Macs is AutoCAD. At the moment, the developers Autodesk only offer a Windows version although you can sign-up to get notified when the Mac version is released later this Fall.
If you're in desperate need of AutoCAD until then, or would like to try a few alternatives, here are 5 great alternatives:
AutoCAD in Parallels This isn't an ideal solution but until the Mac version is released, it's probably the best way to get yourself familiarized with the program using the free trial. It will however put an awful lot of stress on your system so make sure you have enough RAM (I'd recommend at least 4GB). File browsing can also be painfully slow.
HighDesign Although it's only 2D, HighDesign is one of the most powerful and AutoCAD like applications on Mac. HighDesign is suitable for everything from architectural design to construction and it features an extensive set of drawing and editing tools, a context-sensitive interface, sophisticated project management features, and specialized functions.
Google Sketchup As you'd expect from a Google product, there's a refreshing lack of technical jargon in Google SketchUp but that doesn't mean it lacks power. There are plenty of helpful hints and guides throughout too helping you get to grips with 'snapping' when you draw rectangles, circles and other shapes. Although if you're going to use it for professional use, you'll probably need to upgrade to the Pro version.
Intaglio Intaglio is a drawing and illustration application exclusively designed for Macs that makes complex technical drawing or illustration an absolute breeze. It illustrates diagrams in 2D allowing you to easily add graphics, text, color, and scripting. If you've previously been drawing in a different application, then Intaglio will convert it.
VectorDesigner As the name suggests, VectorDesigner is dedicated to all things vector and offers a simple, multi-windowed interface from which you can use all sorts of tools and shapes like rectangles, stars, polygons or bezier creations. Boolean tools offered by the program are easy to work with and let you combine your different shapes in all sorts of ways. VectorDesigner is ideal for creating posters, stickers, t-shirts etc.