About 80% of Internet content is not indexed by Google or other major search engines. Because normal search engines only cover a small part of the web, one might understand the logic in using search engines that can access the deep or "invisible" web.
Voice of the Shuttle Allows users to search a large index of humanities related topics.
The WWW Virtual Library Started by Berners-Lee, inventor of the World Wide Web, this tool allows users to drill down by subject to narrow their search.
USA.gov Search the government, including its agencies. This is a good way to look for grants and financial assistance.