Some of you probably remember the drawing software Diagram on the NeXT computer. Years ago I used that to draw all the graphics for my diploma thesis. Since then I have never found such a good drawing program. Now I stumbled over
OmniGraffle and it looks like this is the successor of diagram. I downloaded the professional version to try it out and the very first steps already look familiar. When you add a few shapes on screen, it just looks good. PDF export works also like a charm and it has a SVG export as well. The latter two are very important for me, as I want the best quality of the drawings when writing a book or an article.
So if you need a drawing program on the mac you should check out OmniGraffle - this is definitively a good option.