Uncovering the Hidden Web, Part I: Finding What the Search Engines Don't. This is an interesting article on finding information on the Web that the big (and little) search engines tend to miss. It is a little dated but still worth reading.
From the site:
Currently, the World Wide Web contains an estimated 7.4 million sites (OCLC, 2001). Yet even the most experienced searcher, using the most robust search engines, can access only about 16% of these pages (Dahn, 2001). The other 84% of the publicly available information on the Web is referred to as the "hidden," "invisible," or "deep" Web.
Despite the explosion in Web content, commonly used search processes have not changed significantly since the Web's inception. Information is commonly found now as it was ten years ago, with directories and search engines. But the ever-quickening pace of the World Wide Web's growth demands an expanded set of search tools and skills. This article provides tips on augmenting traditional search techniques with knowledge of the hidden Web, helping readers to access some of the Web's most valuable content.