Common Graphics Utilities for Linux

ImageMagick

Online Documentation: http://www.imagemagick.org/script/command-line-tools.php

How to downsize a whole directory of graphics

How to convert a color graphic (e.g. .pdf or .ps created by Sweave) to grayscale and still have it be publication quality

Tip #1: Use "convert -density" to convert a vector graphic to a raster graphic at supplied density, say 300dpi.

Gimp

Online Documentation: http://docs.gimp.org/2.6/en/

Scribus

Online Documentation: http://docs.scribus.net/

Inkscape

Online Documentation: http://www.inkscape.org/doc/index.php?lang=en

Graphviz

Online Documentation: http://www.graphviz.org/Documentation.php

Vector Graphics http://en.wikipedia.org/wiki/Vector_graphics