Quantum GIS (QGIS) is a user friendly Geographic Information System that 
runs on Linux, Unix, Mac OSX, and Windows.  QGIS lets you browse and create 
map data on your computer.  It supports many common spatial data formats 
(e.g. ESRI ShapeFile, geotiff).

This requires proj, geos, gdal, R, gsl, and numpy. 

Optional dependencies include postgresql, postgis, and gpsbabel.