While looking for something for another thread, I found [link|http://c2.com/cgi/wiki?GraphViz|this]:

This is my first attempt to use GraphViz to trace links on wiki. Here I chose to follow the links to the two largest pages cited on any given page. I'm thinking the two most recently edited pages might be an even better choice.

And from that, I found [link|http://c2.com/cgi/wiki?VisualizeTheWiki|this]:

This is a compelling idea, one that has been explored in the hypertext world almost since its inception. While it has great appeal, a practical realization has so far proven to be unrewarding. The difficulty is that our minds, when we construct these visualizations, are much better at abstracting "noise" than any of the tools available to us at the moment. Thus, naive attempts to draw unfiltered graphs of the nodes and edges of a hypertext quickly degenerate into meaningless hairy blobs. The interesting part, then, is to discover algorithms for discovering which nodes and links are "interesting" -- and to find ways to present them on finite screens that convey meaning to a user.

and from there, [link|http://usemod.com/cgi-bin/mb.pl?TouchGraphWikiBrowser|this]:

The TouchGraph WikiBrowser is a quick demonstration of how TouchGraph can be used to visualize a Wiki. The current demo renders the MeatBall Wiki, and EmacsWiki LinkDatabase s, but any database encoded in a similar format (see WikisWithLinkDatabases) could be displayed.