Although I'm loving my work in reference, readers' advisory, audio books, and outreach to the homebound, my first love (and internship) was cataloging. After all, if the items in the library aren't cataloged appropriately, it doesn't matter what we own, no one will ever find it.
Some great resources for catalogers:
A Webinar from the Northeast Kansas Library System on getting started in copy cataloging, about 1 1/4 hours long.
The Idaho Commission for Libraries has a series of hour long online courses called ABLE, there's a sequence on collection development, another on reference interviews and a third in cataloging. If you live in Idaho you can get a continuing education certificate for the courses.
ALA's Association for Library Collections and Technical Services (ALCTS) has a series of free webinars on cataloging in their archives.
School Library Journal's article Six Tools to Simplify Cataloging provides links to some great cataloging tips and tools.
025.431: The Dewey Blog "Everything you always wanted to know about the Dewey Decimal Classification system but were afraid to ask ..."
Classify "An experimental classification service" from OCLC. A great spot to figure out how books are being classified by other libraries.