Usability for Nerds/Web design/Accessibility
It is a good idea to make your web pages accessible to handicapped people, even if this is not your primary target audience, because the guidelines listed below have beneficent side effect that will improve the usability to other users as well. Another interesting side effect comes from the observation that the kind of barriers that prevent blind people from reading your pages also prevent search engines from reading your text. In other words, a page that is accessible to blind people is also more likely to be found by a search engine.
Some guidelines from the Web Accessibility Initiative of the World Wide Web Consortium:
Text format. Don't use graphics for making text. Don't make ASCII art. Avoid file formats that can't easily be converted to plain text.
Images and animations. Use the "alt" attribute to describe the function of each visual element.
Image maps. Use client-side map and text for hotspots.
Multimedia. Provide captioning and transcripts of audio, and descriptions of video.
Hypertext links. Use text that makes sense when read out of context. For example, avoid "click here".
Page organization. Use headings, lists, and consistent structure. Use Style sheets for layout and style where possible.
Graphs and charts. Summarize or use the "longdesc" attribute.
Scripts, applets, and plug-ins. Provide alternative content in case active features are inaccessible or unsupported.
Frames. Avoid frames, or make a "<noframes>" alternative and meaningful frame titles.
Tables. Make line-by-line reading sensible. Summarize.
Drop down menus. See the discussion at terrillthompson.com/blog/474.
See also the general page on accessibility.