Free Plotting Tools

Grace
http://plasma-gate.weizmann.ac.il/Grace/

WinDIG
http://www.unige.ch/sciences/chifi/cpb/windig.html

LabPlot
http://labplot.sourceforge.net/index.html

Open Directory
http://www.dmoz.org/Science/Math/Software/Graphing/

QtiPlot
http://www.opendesktop.org/content/show.php/QtiPlot?content=14826