Just when I needed it most, Germany's CadSoft Computer GmbH made their awesome PCB design,
Schematic and Board Layout, and Autorouter Software available for the Mac.
CadSoft's German site:
http://www.cadsoft.de/
CadSoft's US site:
http://www.cadsoftusa.com/
Their EAGLE Layout Editor is an easy to use, powerful tool for designing printed circuit boards (PCBs). Best of all, the EAGLE Light Edition can be used for free!