If you haven't tried it lately, I recommend you give GRASS a whirl. While earlier versions were a mess of imploding modules and inscrutable dialogs, Version 6.4 has many binaries for the major platforms and lots of deep functionality. Check it out at: http://grass.fbk.eu/Mac OS X binaries are available at: http://www.kyngchaos.com/software/grass (just needs GDAL, Freetype and cairo frameworks to install -- links on the KingChaos site).
You also should check out the newest version of Quantum GIS (QGIS). The latest release (1.6.0) is "Copiapó" is getting to be pretty solid. http://www.qgis.org/
While you are at it, download the newest version of Google Earth (6.0) which now boasts 3D trees. Im not sure why we need 3D trees but what the heck. Actually, the better integration of historical imagery makes this a very useful release.