Looking at sites that work is more useful than reading the standard, because the standard tells you what to satisfy and an example shows you what it looks like when somebody has. The examples worth studying are rarely the ones with an accessibility badge; they are ordinary commercial sites where the keyboard path is obvious and the markup is boring. This page is what to look for and how to run the same checks on a site you admire in about ten minutes.
How to judge a site in ten minutes, without taking their word for it
Tab through it: can you always see where you are, can you reach the menu, does the modal return focus. Run a scanner over the home page and one deep page. List the headings and see whether the structure reads. Do that on any site claiming accessibility leadership and you will find the claim is true perhaps half the time, which is itself informative.
The three things the good ones share
Boring markup: real buttons, real labels, real headings, very little ARIA. A visible focus style that is part of the design rather than an afterthought. And content that is written to be scanned: short link text that makes sense alone, headings that describe rather than tease, and images whose alt text says what matters about them.
What not to copy
The badge, the widget and the statement claiming full conformance. On the worked example a site with 401 open issues could install all three this afternoon, and none of them would change a single thing a user experiences. Copy the markup and the focus styles instead.
Questions people ask about accessible websites
Are there certified accessible websites?
No, there is no certification. There are sites that pass an audit at a point in time, which is a different and more honest claim.
Should we publish examples of our own?
Publish the statement and the known issues instead. Examples age; the statement is dated on purpose.
What about government sites?
They are often good on structure and weak on newer components, which makes them useful for the basics and less so for a modern application.