Keep in mind that these are general Catalogues, not specialized or category-specific Catalogues. Note also that there are popular alternatives to Catalogues, such as search engines.
About A well-presented and useful information source combining expert guides and powerful search facilities. Excellent for general research.
Britannica An excellent general research resource, the site is essentially the encyclopaedia tied to a well-presented search engine. One criticism is that it seems to work only with Netscape or Internet Explorer browsers.
Yahoo The granddaddy of them all. Combines a traditional word search with a wide range of categories compiled by human researchers. Highly relevant results, but can be quite out of date, owing to the time it takes to catalogue new entries.
MISCELLANEOUS RESOURCES
Copernic 2000 Not a search engine, but search-engine software. Download and install, and it will send off queries to all the main search engines. Advantages include the ability to retain queries for further use and a winning report function that displays results in an easy to read format.
Ditto An excellent picture searcher that is fast and comprehensive. It provides thumbnails of the actual images, so it's perfect for finding photographs or pieces of artwork in a hurry.
Metacrawler Sends search request to several of the largest search engines from the one website. Useful, but the results won't necessarily be as relevant as using the engines individually.
UKplus A UK-specific, British-designed and -run service.