Accessibility checkers
CSS Validator (W3C)
Cynthia Says
Hermish.com: free web accessibility tool designed to help you bring your web site up to standards outlined by The World Wide Web Consortium (W3C)
HTML Validator (W3C)
Step 508: A tool for prioritizing Web site accessibility problems
Software specific guidelines
Adobe
Macromedia
Microsoft
Illinois Accessible Web Publishing Wizard for Microsoft® Office
Training resources
Adobe
Freedom Scientific
* Accessible Documents with JAWS
Karlen Communications
* Creating More Accessible PDF Documents
* Creating More Accessible Web Pages
Section508.gov
Web Site Accessibility How to create, modify, and check your web pages to make them “universally accessible†(online class)
Articles
Disabled Accessibility, the Pragmatic Approach, by Jakob Nielsen
Design/information design
Edward Tufte Books)
Universal Design Education Online
Usability
All Things Web: The Usable Web
Designing More Usable Websites
Useit.com (Jakob Nielsen)
Usability.gov - Newsletters and Publications