DocBook - Raymond Yee's Wiki

DocBook is a SGML/XML specification that started off being used primarily for technical documentation. It is useful for lots of reasons -- it's being heavily used (as far as I can see) -- and it offers a XmlSpec representation of book-like things.

docbook.org
docbook wiki
OASIS page
Online DocBook Validator and XML -> HTML/PDF Transformer

tutorial

I'm particularly interested in the BibliographicMetadata functionality of DocBook.