GIS on the Macintosh

Grass

Command line driven

OpenOSX port of Grass: http://openosx.com/grass/ CD is $50 You can also get Grass for free from http://wwwamb.bologna.enea.it/forgrass/)

OpenOSX specializes in porting UNIX software to the Mac. They also have Wintel, a virtual machine for running Windows and Linux on the Mac. See Virtual machines on the Macintosh

uDig

http://udig.refractions.net/

Looks nice but so far I can't get it to open shapefiles, this could be a serious drawback.

Orbit

http://www.orbitgis.com/ (Orbit GIS)

Low cost (EU299) enterprise program, free Orbit Explorer viewer

Support for Mac OS X, Windows, Linux

Links

Links I have not followed up on yet.

http://qgis.org/ (Quantum GIS)