Regarding examples of accessible websites, I would suggest the Accessiweb gallery: Accessiweb is a reference list 100% based on WCAG2, and they deliver quality marks (the "Accessiweb label") upon website owners solicitation. The website undergoes a thorough manual review (on a carefully defined 10-page sample, more or less), and it gets the label only if it's flawless on every page. The level is reflective of the number of defects found and not corrected. Bronze is exactly equivalent to level A, Silver to AA, and Gold to AAA. So getting a Silver label means all A and AA tests were passed on all of the sample. Bronze, two stars: All A tests were passed, plus 50 to 75% AA tests. And so on.
You probably won't have to check your site with all of the available evaluation tools out there, but it is a good idea to do so for the most common web browsers. Just as accessibility software makes it easier for people with disabilities to navigate the Internet, these tools make it easier for developers to ensure accessibility from the start. When you think you've mastered it, go back through the Section 508 compliance checklist to ensure you've met every goal.
The ADA requires that title II entities (State and local governments) and title III entities (businesses and nonprofit organizations that serve the public) communicate effectively with people who have communication disabilities. The goal is to ensure that communication with people with these disabilities is equally effective as communication with people without disabilities.