The WWW Virtual Library is an excellent "distributed subject tree" directory, entirely based at colleges and universities around the world, each one maintaining an annotated links list for a separate category.

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The Internet Public Library is an integrated "subject tree" directory, organized in "library" form. The IPL has merged with the Librarians' Internet Index, and the result is called IPL2.

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Originating as the "Bulletin Board for Libraries", BUBL is the premier subject tree based in the UK, and contains links to a higher percentage of UK sites than other directories. The search results list both specific websites and BUBL directory categories. Advanced Search

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Infomine is an academic subject directory containing over 20,000 good links for scholarly research, based at the U. of California at Riverside.

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Traffick.com is a site dedicated to news and information about major web portal sites.

About.com (formerly The Mining Company) is a collection of over 700 topical subject guides to Internet resources, each maintained by an expert in the field.

DMOZ Open Directory is similar to Yahoo's directory, but with better site descriptions, Netscape's Open Directory Project is a directory of almost 2 million sites maintained by over 26,000 volunteer editors, and freely licensed to other sites. It is more comprehensive and less selective than the other directories listed here.

Other Portals:

Michigan eLibrary
Yahoo
Netscape
Microsoft Network (MSN)
Lycos
Excite
MyWay.com