Another interesting one, though it's more dependent on user input.
Blogtree tracks the process by which blog authors inspire and encourage new blogs. When I registered, I was able to specify which blogs I considered to be my "parent" blogs--those which inspired me to create my own blog. (Different from those that I read regularly, though there's obviously some overlap.)
Based on that input, it generates a family tree for me, which includes a list of "siblings"--other blogs with similar genealogy. If my blog inspires a friend or reader to create his or her own, it would then become one of my "child" blogs. Hmmm. Not as awe-inspiring to me as things like allconsuming or waypath, but fun and informative nonetheless.
