Quick Tips to make Accessible Web Sites
W3C Web Accessibility Initiative

For complete guidelines & checklist: http://www.w3.org/WAI

- Images & animations. Use the ALT attribute to describe the function of all
  visuals. 

- Image maps. Use client-side MAP and text for hotspots.

- Multimedia. Provide captioning and transcripts of audio, descriptions of
  video, and accessible versions in case inaccessibel formats are used. 

- Hypertext links. Use text that makes sense when read out of context. For
  instance, do not use "click here."  

- Page organizations. Use headings, lists, and consistent structure. Use CSS
  for layout and style where possible. 

- Graphs & charts. Summarize or use the LONGDESC attribute.

- Scripts, applets, & plug-ins. Provide alternative content in case active
  features are inaccessible or unsupported. 

- Frames. Label with TITLE or NAME attribute.

- Tables. Make line by line reading sensible. Summarize. Avoid using tables
  for column layout. 

- Check your work. Validate the HTML. Use evaluation tools and text-only
  browsers to verify accessibility. 

http://www.w3.org/WAI/References/QuickTips