These are designed to guide you to the appropriate search engine, not to the specific information that you may need. A directory of search engines across academic and popular topics. An extensive but organized list that has databases geared for research and academics. A good source for links to general reference sources. Direct Databases Much of the invisible web consists of databases, or collections of computer files, that have their own search engines.
Some sites offer free information while others require registration, a fee, and a password.
This is sampling of some databases by subject. Some of the richest documents on the web are not in HTML, but in Adobe's PDF format. These groups cover a wide variety of topics, both for professional and personal interests. You can ask questions of the experts and read the answers to questions that others ask. You can join a discussion group or search the archives to eavesdrop on conversations.