The ADAAG Manual was created by the Access Board of the Architectural and Transportation Barriers Compliance Board as companion information to the Americans with Disabilities Act Accessibility Guidelines (ADAAG). It explains and clarifies many of the requirements of the ADAAG, and gives insight on the intent of the requirements. I recently found a downloadable version available online. You can download it here by clicking on the link at the top that says “ERIC Full Text”.
The ADAAG Manual doesn’t include the text of the ADAAG, but you can download the ADAAG on the ADA.gov site.
The proposed revisions to the ADA regulations are also available for download. Look for the links under “Proposed ADA Standards for Accessible Design“.