CompletePlanet - Listing of dynamic searchable databases with documents that cannot be crawled or indexed by surface web search engines.
Deep Web Research - Monitors deep web research resources and sites on the Internet.
DeepWeb.com - Overview of the deep Web problem, and solutions for accessing it.
Invisible Web Directory, The - Companion to the book by Chris Sherman and Gary Price provides information about searchable databases and specialised search engines.
MetaQuerier Project at UIUC - Research projects to help users in finding and querying online databases effectively and uniformly.
Wikipedia: Deep Web - Overview and links about the hidden, or invisible, web.
Yahoo! Search Subscriptions - Service to search information on password-protected subscription sites such as LexisNexis, the Wall Street Journal, and Consumer Reports.