There are several resources regarding accessibility guidelines, including:
- W3C: Web Content Accessibility Guidelines 1.0
- 14 guidelines with checkpoints available at http://www.w3.org/TR/WCAG10/
- Full checklist available at http://www.w3.org/TR/WCAG10/full-checklist.html
- WCAG 2.0 (draft) available at http://www.w3.org/TR/WCAG20/
- More guidelines available at http://usableweb.com/topics/000262-0-0.html