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The BBC's Mobile Accessibility Standards & Guidelines: http://www.bbc.co.uk/guidelines/futuremedia/accessibility/mobile/about
Books
There are a number of great books on the topic of Web Accessibility. Here are a few of the better ones:
A Web for Everyone by Sarah Horton & Whitney Quesenbery
Accessibility for Everyone by Laura Kalbag
Color Accessibility Workflows by Geri Coady
Inclusive Design Patterns by Heydon Pickering
Helpful Articles
Common pitfalls and misunderstandings in accessibility auditing