Below list some useful tools for automated checking:
Total Validator is an (X)HTML validator, an accessibility validator, a spell checker, and a broken links checker all rolled into one tool allowing one-click validation of your website.
AChecker is a checking tool that checks single HTML pages for conformance with accessibility standards.
WAVE is an evaluation tool that shows the original web page with embedded icons and indicators that reveal the accessibility of that page.
PDF Accessibility Checker (PAC) is a freeware program that provides a fast way to test the accessibility of PDF files.