Another Site
I just found a wonderful resources called invisibleweb.net
Courtesy of the Librarians' Index to the Internet (LII), these Bookmarks for Free, Fast and Factual are the best places to go for specialized web sites. A reference librarian's dream!
Scholarly Electronic Publishing Resources includes a wide variety of ebooks, image resources and other types of digital material to poke through.
My latest find is:
How to Find the Invisible Web
The "invisible web" is what you cannot retrieve ("see") in the search results and other links when you use typical search engines. Most of the invisible web is made up of the contents of thousands of specialized searchable databases that you can search via the Web. The search results from many of these databases are delivered to you in web pages that are generated just in answer to your search. Such pages very often are not stored anywhere in particular.