I've had the pleasure of collaborating, first at Machina Sapiens [http://www.documens.com/francais/francais.htm] and later at CRIM [http://www.crim.ca/], with one of the best specialists of complex information visualization, my friend Luc Beaudoin [http://pages.infinit.net/lbeaudoi/].
He invented an advanced representation technique for display of hierarchical information, before tackling even more complex problems for Nortel Networks [http://www.nortelnetworks.com/]. (His latest baby: PPCG [http://www.patentstorm.us/patents/6854091.html]) I realized, with Louis Vroomen [http://www.pyrais.net/portfolio/crim/index.shtml], the first incarnation of his work on hierarchies, under the name of Cheops.
Nowadays, I am mostly interested in applications of visualization to deliberation. But that will not stop me from working with GraphViz, GXL, or SVG...