Concept mapping versus topic maps and mind mapping http://en.wikipedia.org/wiki/Concept_mapping#Concept_mapping_versus_topic_maps_and_mind_mapping
List of concept mapping and mind mapping software http://en.wikipedia.org/wiki/List_of_mind_mapping_software
See also: http://www.delicious.com/tag/mindmap
I think I would vote for Mindjet.com MindManager (mainly because you can export fromhttp://www.wikisummarizer.com into Mindjet).
Data visualization is a related field, which might give you some more ideas.
http://en.wikipedia.org/wiki/Data_visualization
Data visualization software
http://en.wikipedia.org/wiki/Data_visualization#Data_visualization_software
(Disclaimer: I make artificial minds at http://meta-guide.com ..)