When you mention QGIS, you should also mention GDAL, JTS, udig, geoserver, open stree maps, open scene graph, FWtools etc. Open source GIS has awesome list of projects and people, QGIS being only one of them. It really fascinates me.
and also that qgis installs 1g+ of all these goodies tied together.
GDAL should be front and center. It's the xkcd 2347 of earth observation and geographical information systems
The sqlite db alone that's packaged with PROJ is a pillar of knowledge that one can only marvel at. The most authoritative and wide-ranging collection of projection/datum information I'm aware of.