You may use the checklist provided in the Tools section of this site. It is based on the W3C guidelines but includes additional elements as well. You may also use the W3C checklist
http://www.w3.org/TR/WCAG10/full-checklist.html.
If you are using the W3C checklist and believe your site has followed the W3C's Web Content Accessibility Guidelines (WCAG), you may use the WCAG Conformance Logos to demonstrate this.
Use of this logo is not based on a validation test but on your own assessment of which priority levels of the Web Content Accessibility Guidelines 1.0. your site satisfies. For more information on this go to the Conformance Logo section of the W3C site: http://www.w3.org/WAI/WCAG1-Conformance