Popular Search Engines & Directories 

• Ask Jeeves
  Ask Jeeves lets you type a question in plain English and get back easy-to-understand answers. It also has the most integrated search interface of the popular search engines
• Google
  Needs no introduction. Index of 10 billion web pages. Google Rules!
• MSN
  Microsoft's attempt at a search engine is average.
• Yahoo Search
  Second only to Google.

Meta-Search Engines  

• Meta-Search Engines
  They search many engines at once, and combine the results. This page showcases the best of them.
• Meta-Meta Search
  This is the only way to search 9 meta-search engines at once, the web's only meta-meta-search (that I know of).

Useful Links 

• A map of search engine relationships. Someone made a Flash version.
• Long Word Searching Showdown - Greg Notess reports "The search engines have some limits as to how long a word they will search. This table shows the search engines, in descending order of the ones that can find the longest words.".
• Relative Sizes of search engines
• Thumbshots Ranking - lovely graphic comparison of search results. See how little overlap there really is...
• Search Engine Ratings - from Nielsen NetRatings
• Search Engine GraveYard or this article, Where are they now?
• Ultimate Search Engine Links - over 1,000 categorised links
• Search Engine Colossus - search engines from over 190 countries