blockdiag and its family generate diagram images from simply text file:
Generates beautiful diagram images from simple text format (similar to graphviz’s DOT format)
Layouts diagram elements automatically
Embeds to many documentations; Sphinx, Trac, Redmine and some wikis
Enjoy documentation with blockdiag !
Google Groups: http://groups.google.com/group/blockdiag-discuss/topics
Interactive Shell: http://interactive.blockdiag.com/