Hytelnet on the World Wide Web
A listing of library catalogs from the Americas, Europe, Middle East, Asia, Pacific, and South Africa, plus other library resources.

lib-web-cats
Searchable database of over 4,500 library web sites and online catalogs worldwide.

Libdex
A worldwide directory of library homepages, web-based OPACs, Friends of the Library pages, and library e-commerce affiliate links.

Libraries of the World and Their Catalogues
Links to national, academic and public libraries and their catalogues.