These draft guidelines (December 2008) produced by the World Wide Web Consortium (W3C), explain how to make Web content accessible to people with disabilities. The guidelines are intended for all Web content developers (page authors and site designers) and for developers of authoring tools. The primary goal of these guidelines is to promote accessibility. However, following them will also make Web content more available to all users.
http://www.w3.org/TR/WCAG20/