While doing some research on accessibility this evening, I came across a free e-book on accessibility called Dive Into Accessibility (available in HTML and PDF format).

Although the book appears to have been written in 2002, it still offers a great deal of good, valid information for today’s Web developer. Some of the information is a bit outdated, but the majority of it still holds up today. If you’re looking for resources on accessibility, be sure to check this one out.