Check out these interactive maps. How come I didn't find this sooner? Now make each link carry its meaning (ie. the nature of the relationship between two companies) and this will be the stuff of my dreams.
02/09/01 update: see also CompanyClique.
05/10/01 update: NameBase does social network diagrams through proximity searches.
07/13/01 update: TouchGraph, or Inxight meets TheBrain.
07/20/01 update: TheyRule, maps of board members (thanks Jason).
12/23/01 update: The Big Ten (on media concentration).
01/29/05 update: Finding Mavens in Usenet, Graph del.icio.us related tags.