Not sure it would yield any useful results, but have been thinking about a no-index search engine for a while to help find obscure or otherwise hidden information. If one exists or you build one let me know.
Showing all the lower ranked sites would be pretty cool. A lot of blogs would probably end up there, especially if they don't care about pagerank like me.
A search engine that shows only urls that are not indexed b google / another one that gives you the websites with lower pagerank