Validation Graph of Flickr.com
Centered on my photos page :)
This is a map of the Flickr site, where they grey circles represent URLs that end in a slash, and the blue circles are (I think) images.
Based on Sala's Web Sites As Graphs, this is a crawler that visualizes the validation profile of the pages in a Web site. As it traverses links, it also draws a clear image of the IA (the "site map"). It's hard to think of another free tool that gives this kind of immediate, visual insight into how a site is organized. Definitely not production-ready. And, of course (its a tree graph), it doesn't show all the links between pages.