Finally, WA11Y is another top ADA compliance plug-in to consider. A toolbox of resources to help you meet most ADA compliance needs, the plug-in packs multiple accessibility tools, each with a unique purpose. Tota11y, the first tool in the box, for instance, annotates all elements of your web pages and identifies any accessibility issues. Another tool in the box, WAVE, performs a detailed accessibility analysis of each page and provides printable reports. Then, you have FILTERS which is used to modify data within Wa11y.
Covered entities are required to provide aids and services unless doing so would result in an “undue burden,” which is defined as significant difficulty or expense. If a particular aid or service would result in an undue burden, the entity must provide another effective aid or service, if possible, that would not result in an undue burden. Determining what constitutes an undue burden will vary from entity to entity and sometimes from one year to the next. The impact of changing economic conditions on the resources available to an entity may also be taken into consideration in making this determination.

Leading web developers have been pioneering accessibility and publishing standards since 1994. In 1999, the Web Accessibility Initiative (WAI) and the World Wide Web Consortium (W3C) created the Web Content Accessibility Guidelines (WCAG). In essence, the people who determine how the internet is written came together to advise web developers on how to make websites accessible not only to people with disabilities, but to all web users, including those with highly limited devices.
Penn in particular nearly made the cut because I really like their keyboard accessibility. It amazes me how few sites provide visible indication of keyboard focus, when it's incredibly simple to achieve (just add a style for a:focus in your style sheet). Penn did this, and consequently it's very easy for sighted keyboard users to keep track of their position as they tab through the page. They also included a keyboard-accessible dropdown menu. However, there are some dynamic features on the Penn home page that really need ARIA markup for full accessibility. They also have a few contrast problems, most notably their slideshow navigation, which is red-on-red:

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.