There are some really good websites out there for catalogers. In general, these sites provide links to important websites, like the Library of Congress page for Librarians, OCLC’s Classify, the Online Audiovisual Catalogers, Cataloger’s Resource Shelf, Cataloger’s Toolbox.
I recently found two more worth adding to the list:
The Catalog Dept. at the William F. Maag Library, Youngtown State University, has a good selection of helpful links at: http://www.maag.ysu.edu/techsvs/cat/newtools.htm.
The University of California, San Diego has a great list of resources for catalogers at: http://tpot.ucsd.edu/msd/catpolicies/cattoolsresources/index.html. They way that they organize the information is helpful because the section for frequently used tools is readily and quickly seen.