I have written elsewhere about choosing tools to make your efforts at designing for accessibility easier. However, since I wrote my article, the W3C has stepped up with Authoring Tool Accessibility Guidelines 2.0. The guidelines give information about making the design tool itself accessible, and what the design tool should do to help the designer create accessible sites.
Color Laboratory — AWARE Center — HTML Writers Guild Look for the link to the web page color filter for access to a tool currently under development that allows you to apply a filter to a page to see how it looks under different types of color blindness.
Accessify.com – all the tools, links and resources you’ll ever need to make your web site accessible. This new site looks like a good addition to the must-bookmark accessibility resources.
Vischeck: Home has a tool to simulate colorblind vision so you can check your contrasts and color use.
Dive Into Accessibility organizes their tips by person, disability, design principle, web browser and publishing tool.
W3C standards call for the use of a ‘longdesc’ attribute for images or other possibly inaccessible page elements. The longdesc attribute in a tag links to an HTML file that gives a long description of the inaccessible element. But browser support for longdesc is still somewhat problematic. So many people are now using a workaround that involves putting a ‘d’ after the element. The ‘d’ is made into a link to the long description. This practice is understood by people who need the long description information.
NCAM/Media Access Generator (MAGpie) This site has a tool that allows you to add captions to three multimedia formats – Quicktime, SMIL, and SAMI.