Free or free-ish:

Plot – http://plot.micw.eu/

Python Graph Library – http://matplotlib.sourceforge.net/

DataGraph – http://www.visualdatatools.com/DataGraph/index.html

ParaView (3D visualization) – http://www.paraview.org/

GraphSketcher – http://www.graphsketcher.com/

R (statistical) – http://www.r-project.org/

Not so free:

Numbers – http://www.apple.com/iWork

Aabel – http://www.gigawiz.com/aabel.html

Citrin – http://www.gigawiz.com/citrin.html

Smile – http://www.satimage.fr/software/en/index.html

Profit – http://www.quansoft.com/