GIMP Plugin Registry

This script generates a poster like the famous Che Guevara one from Jim Fitzpatrick. Copy it into the scripts folder from GIMP, you will find it then under Filters -> Artistic -> Che Guevara.  read more »

This plugin does a pretty good job of eliminating shadows and highlights in photographs. It gives you two layers that basically act like adjustment layers, and changing the opacity will alter the effect.

Implement several different black and white conversions including color filters

More information:

http://epaperpress.com/psphoto/
http://www.thelightsrightstudio.com