Here is the main one I would use http://joeclark.org/book/sashay/serialization/
This link and many more are on this list of Web accessibility resources:
http://whdb.com/2008/100-killer-web-accessibility-resources-blogs-forums-and-tutorials/
Some that are of interest:
http://juicystudio.com/services.php this is a tester we can run to see where we need to work on accessibility
http://www.standards-schmandards.com/2010/fangs-moving-to-mozilla/ screen reader emulator
http://www.w3.org/TR/WAI-WEBCONTENT/ Web Accessibility Guidelines
http://www.alistapart.com/topics/ This is a list of topics to help build more accessible code
http://www.webjunction.org/accessibility/articles/content/432159 retrofitting your site.
http://www.diveintoaccessibility.org/ a nice tutorial on why accessibility is important and how to get started