Whether you're new to web accessibility or not, this book by Jim Thatcher, Michael R. Burks, Christian Heilmann, Shawn Lawton Henry, Andrew Kirkpatrick, Patrick H. Lauke, Bruce Lawson, Bob Regan, Richard Rutter, Mark Urban, and Cynthia D. Waddell -- with a forward by Molly Holzschlag - will have something for you. It covers in detail some of the finer points so that your next web site will be better then your last and that it'll be in compliance. The book's topics (sections) include the following:

The Impact of Web Accessibility: Basic understanding and concepts, the law, and enterprise implementation.

Implementing Accessible Web Sites: Technologies overview, assistive technologies, content accessibility, accessible navigation, data input, CSS, accessible JavaScript, Flash, and PDFs, testing, intro to WCAG 2.0, and a case study (university web site redesign).

Accessibility Law and Policy: US laws, worldwide laws, various appendixes.

The information in this book is available on the web, but it's variable and fragmented. This tome puts it all together in a single resource and does so with the voice of authority. Thus, if web accessibility is your cup of tea, your bread and butter, or just something you want to understand better, this book is a must-read. I'm giving it five stars as I think it's the best in its class.