I’ve created a new listing of over 80 free mapping programs including GPS, GIS, LiDAR, CAD, Statistics, Image Processing, and Remote Sensing applications. The list is available at http://www.FreeMappingSoftware.org/ (http://www.freemappingsoftware.org/) .

Wow, that's quite a collection. Thanks!

Do you have any sense of what packages are most popular and useful and/or which ones are no longer being maintained and developed?

Thanks again!

3DEM
ArcGIS Explorer
CADX11
DG Terrain Viewer
DielmoOpenLiDAR
DNR Garmin
Easy GPS
E-Foto
FMaps
FreeCAD
FugroViewer
Fusion (LiDAR)
GDAL (Geospatial Data Abstraction Library)
Generic Mapping Tools
GeoMagas
GEON Points2Grid Utility
GeoNetwork
GeoTools
GeoVista
GIMP
GISToolkit
Global Land Cover Facility (Data)
GLOVIS (Data)
Google Earth
Google Sketchup
GPS Babel
GPS Manager
GPS TrackMaker
GPS Utility
GPS3D
GPSDrive
GrADS
GRASS GIS
gvSIG
ImageJ
ImageMagick
Inkscape
Integrated Land and Water Information System (ILWIS)
JUMP Unified Mapping Platform
Landserf
LizardTech GeoViewer
Lviz LiDAR
Mapbender
Mapbuilder (Project completion)
MapGuide
Mapnik
MapServer
MapSphere
Mapyrus
MARS Viewer (LiDAR)
MB System
MySQL
Natural Resources Database
Nunaliit Cybercartographic Atlas Framework
Open Visualization Data Explorer
OpenEV
OpenJump
OpenLayers
OpenMap
Opticks
Parallel Database System for GIS Applications
Paraview
PostGIS
Quantum GIS
Rapidform Explorer
Shapefile Coordinate Transformation Utility
SharpMap
Simple Map Server
Spatial Analysis and Modelling Tool
SPRING
StatPlanet
StereoScan
TARDEM
Terragen
TerraView
Thuban
Triangle
Triangulated Surface Library
uDig
VG4D Viewer
Vis5D
WinDisp
WINGS 3D
WorldKit

As of last weekend all the applications were active except for MapBuilder which is still available but not being developed any more. It’s hard to indicate which ones are the most popular because each one seems to specialize in its own area, so you will just have to find one that fits your needs and go with it.

I spot a few I wouldn't think of as mapping programs, though I can see you could make cases for each

GIMP
ImageMagick
InkScape
MySQL

Yes, I included those ones because Cartographers often use them as parts of their workflow (and they are just so useful).