ergophobe - 3:21 pm on Sep 15, 2010 (gmt 0)
Well, as a starting point, if you haven't already, you'll probably want to peruse the Web Accessibility Iniative pages at W3C.
That's sort of a portal for such thing. In particular, look at the Web Content Accessibility Guidelines
which include some handy checklists and guides on how to become compliant.
That will also lead you to all sorts of tools that you can use
The classic one is Bobby (commercial) and WAVE is a nice online tool (free).
There are a variety of specific tools, like contrast analyzers (like this one [visionaustralia.org.au]) and so forth for specific tasks.