Free of charge Resources of available Webmaster Tools and Accessible Online Tests on the Internet
Search Engine Watch
DomainGo Inc.: IP Search Engine.
BLOONATIC LLC Search Engine Consulting: The Chicken's Guide To Search Engines. An annotated link directory. Use the right online tools, e.g.: "Is my web page valid HTML", "Search engine optimization", "How do I improve my web site's ranking", "Submit your URL", "Verification" (did the optimization work, did my ranking improve), and "more about search engines".
Jim World, Ultimate Bulletin Board: Search Engine Forums. Discuss the search engines and get answers. A different Forum for each search engine.