What are the best resources for designing "accessible" interfaces?

I'm reading Steve Krug's book "Don't Make Me Think! A Common Sense Approach to Web Usability" and there are a few good sources that he points to that will help designers design more accesible interfaces. Here are some of the ones from the book.

• Guidelines for Accessible and Usable Web Sites: Observing Users Who Work With Screen Readers - Published in the ACM Magazine, Interactions (November-December 2003). With permission from ACM, Janice Redish has made it available for personal use, so please do not redistribute.
• WCAG (Web Content Accessibility Guidelines) Validator
• Building Accessible Websites by Joe Clark
• Constructing Accessible Websites by Jim Thatcher et al.
• Maximum Accessibility: Making Your Web Site More Usable for Everyone by John Slatin and Sharron Rush

What else is out there? For software? For physical interfaces?