Colleague Owen Densmore writes:

"Every now and again I check into the latest GIS open software. Last
time I looked, the uDig package (an Eclipse "rich client") was quite
good.

But in the mean time, QGIS as gotten quite good.
http://qgis.org/
It has a much improved UI (Qt window system) and has a fairly
extensive set of file formats it handles well. And its built on top
of the standard C/C++ GIS tools like GDAL and OGR (raster and vector
formats).

And for the python fans, its got a python plugin feature.

This might be quite useful: command-line/python access to the
libraries for custom scripting, yet a very usable GUI front end.

-- Owen

-tj