Important!: It is recommended that you visit the homepage of the software you are interested in and download the latest version from there.
For Mac OSX many of the most common apps most recent versions are at http://www.kyngchaos.com
Install the base packages (Frameworks) first, followed by the support packages, and finally the end-user programs. The base packages must be installed in order.
Not all Frameworks and support packages are needed for all end user programs. Consult the above website for details.
The framework packaging method is a bit more trouble up front, but ensures the minimum amount of disk space is used by programs which share common support libraries, and that these components can be safely upgraded in future without rendering the other programs unusable.
http://www.kyngchaos.com/files/software/frameworks/GDAL_Complete-1.10.dmg
http://www.kyngchaos.com/files/software/frameworks/FreeType_Framework-2.4.10-1.dmg
http://www.kyngchaos.com/files/software/frameworks/cairo_Framework-1.12.2-1.dmg
http://www.kyngchaos.com/files/software/frameworks/GSL_Framework-1.16-1.dmg
http://www.kyngchaos.com/files/software/frameworks/TclTk_Aqua-8.5.8-2.dmg
http://www.kyngchaos.com/files/software/frameworks/Spatialite_Tools-3.0.zip
http://www.kyngchaos.com/files/software/frameworks/rgdal-0.8.8-1.dmg
http://www.kyngchaos.com/files/software/postgresql/PostgreSQL-9.2.4-2.dmg
http://www.kyngchaos.com/files/software/grass/GRASS-6.4.3-1-Snow.dmg
http://www.kyngchaos.com/files/software/postgresql/PostGIS-2.0.3-4.dmg
http://www.kyngchaos.com/files/software/qgis/QGIS-1.8.0-2.dmg
http://udig.refractions.net/files/downloads/udig-1.3.2.macosx.cocoa.x86_64.zip
http://download.osgeo.org/ossim/installers/mac/imagelinker-1.7.15-appbundle.dmg
http://download.osgeo.org/ossim/installers/mac/ossimplanet-appbundle-1.8.4.dmg
http://github.com/downloads/mapbox/tilemill/TileMill-0.10.1.zip
http://grassmac.wikidot.com/downloads