Today, George Silva asked on the OSGeo Discuss mailing list for some details on history of Free and Open Source Software for GIS. Shortly, the discussion has turned into a very interesting brainstorm session resulting in detailed overview of FOSS4G roots and chronology.
More on Brief history of GIS OSS (bit off topic?)
Update: 22-08-2008:
Based on the discussion about history of FOSS4G, dedicated article on OSGeo Wiki has been started: Open Source GIS History