The Web Accessibility Checker is a free validator available from the Adaptive Technology Resource Center in Ontario, Canada. The Web Accessibility Checker can check your website for compliance with both Section 508 and the Web Content Accessibility Guidelines.
The Cynthia Says website is a free service that allows you to check your website for Section 508 compliance. Section 508 is the U.S. accessibility law that applies to all websites maintained by the federal government and its contractors. While private websites are not required to comply with Section 508, many of them still use Section 508 as a good overall measure of accessibility.