Plot 3D (Popularity: )
http://www.plot3d.net/ 2D and 3D function graphing. Includes freeware download, and a gallery of output. [Windows 98-XP]
Gnuplot Central (Popularity: )
http://www.gnuplot.info/ Official website for gnuplot 4. Includes downloads, screenshots, documentation, and links to other help and tutorials.
Gnuplot.py (Popularity: )
http://gnuplot-py.sourceforge.net/ A Python package, that interfaces to Gnuplot allowing the use of Gnuplot from within Python to plot arrays of data ...