AIS - Web Accessibility Toolbar: Toolbar aids manual examination of pages for accessibility features. It consists of a range of functions that: identify components of a web page; facilitate the use of 3rd party online applications; simulate user experiences; provide links to references and additional resources.
Anybrowser - screen size testing: Enables you to test how your page appears at low screen resolutions - e.g. webtv, 640x480, 800x600.
ATRC Web Accessibility Checker: Analyses a page for conformance with WCAG 1.0 and 2.0, BITV 1.0, Section 508, and the Stanca Act.
Bobby WorldWide: Validator that checks pages for WAI and 508 accessibility standards.
Color Vision - by Cal Henderson: Test your website foreground/background colors for their contrast and clarity to color blind visitors.
Colorblind Web Site Filter: View your actual web pages through the eyes of visitors with three different types of color blindness.
Cynthia Says Portal: Accessibility agent offering validation for WAI standards and Section 508 compliance. Includes information and news from the Internet Society Disability and Special Needs Chapter.
Erigami Accessibility and Quality Validation Tool: Checks web page accessibility on compliance with WCAG and Section 508, including automatic color contrast validation of text elements. It shows issues on a web page screenshot, measures response and download times of every element.
GrayBit Grayscale Contrast Tool: Converts your page to greyscale to ensure there is sufficient visual contrast between elements.
Hermish: A free on-line accessibility and browser compatibility checker. Hermish will test your web pages for accessibility issues and provide a detailed report.
HiSoftware.Com Accessibility and Quality Tester: Tests to Section 508 and WCAG standards.
Juicy Studio: Colour Contrast Analyser: Uses the W3C algorithm to check for sufficient contrast between background and foreground colours.
Lynx Viewer: Delorie online viewer enables you to view your site in a text browser.
OCAWA Accessibility Validator: Standing for Operational Control and Analysis for Web Accessibility. OCAWA tests the accessibility of your web site using international accessibility standards.
Q42 Color Blindness Check: View your website as someone with color blindness would. Appears to work only in IE. Bookmarklet available.
UITest.com: Site Check: Test your website with the W3C, WDG, ATRC, WebAIM, WebXact, Bobby, Cynthia Says, HiSoftware, Site Valet, Colorblindness filter, and Google Viewer, simply by typing your site address once.
Vischeck: Allows the user to see the world as color blind people see it. Checks by images and urls.
W3C CSS Validation Service: W3C CSS Validation service enables you to check your CSS code for validity, and warns you if you are using browser specific code.
W3C HTML Validation Service: A free service from W3C that checks HTML and XHTML code against the W3C Web Accessibility Guidelines.
Wave: Helps you check if your page is accessible to people with disabilities. New version includes tests for section 508.
WAVE 3.0 Accessibility Tool: Online tool checks page accessibility, displays page with tags to show good and bad points.
Webnauts Net: Offer a combined interface to collection of tools (W3C, CSE, and Cynthia validators, and also a Lynx simulator) for checking adherence to standards, mark-up and accessibility.
Webthing Accessibility Valet: This tool will examine your site, and based on the accesibility level you choose, will provide you with a source code listing with marks next to each element which requires attention.