Use blogs to search hidden web content. A site may not be spidered by a search engine, but someone may well find and blog it. Use BlogDigger, BlogLines, Blogdex.net, blogsearch.google.com to find things indirectly—you’re leveraging the blog experts’s ability to find obscure content. (No time to dig up URLs…)I'm finding this technique very useful, as I alluded in my post on companies banning blogs.
Thanks to Liz Lawley for a most comprehensive write-up.