Carsten Cumbrowski has written a nice piece at Search Engine Journal about the 50 questions that you should ask to evaluate the quality of your website. He groups the questions into categories from Accessibility to Design to Security and even Legal questions. A sampling of questions:
Security: How resilient are forms to special characters? Accessibility: How compliant is the website with W3C coding standards? Valid HTML/CSS? Navigation: Call to action on every page, no dead ends
These are great questions and this is a checklist that should not be ignored when designing a website (and then performing QA on it afterwards).
Forum discussion continues at Sphinn.