Invisible Web (Subject Specific Resources)
The invisible web refers to a group of search tools, whose informational contents are generally not retrieved by any search engines, hence making it invisible to anyone who would use search engines to find it. Generally this group of information is composed of subject specific web sites and searchable databases that provide information on a particular topic.
Although there is no one special trick to finding resources in the Invisible Web, there are ways one can go about finding these resources for their own needs.
The Invisible Web Directory
Librarian's Index to the Internet