I’ve linked to the Library of Congress’ website on standards before. I thought that I would bring it up again. This website is a real treasure trove of information on current standards in cataloging and metadata and crosswalks. Think of PREMIS, MARC21, VRA, METS, or MODS. This page can be found at: http://www.loc.gov/standards/.
Don’t forget to link to their page, Metadata for Digital Content, where you can read about the metadata policies that have developed over the years at the Library of Congress.
This site in combination with LC’s Authorities and Vocabularies website, where headings come with uri’s great for linking data, one can really have ready at hand a number of resources needed for a large variety of cataloging and metadata projects.