Other Useful packages recently discovered.
octave
http://www.octave.org/
Open Source Matlab


Gnuplot
great drawing tool
http://www.gnuplot.info/


Boost, previous Generic Graph Component Library (GGCL), looks like a powerful c++ graph package

PathView

Great 3-D visulization, if we want to build a real cool galaxy of citation network ;-)
http://www.haydenplanetarium.org/hp/vo/partiview/

R
http://www.r-project.org/
statistics package with a good social network analysis module