Cool post. one note on the title attribute - if the link text is descriptive enough you really don't need to add an extra one. Adding it when it's not needed just makes reading the link longer for screen readers. It's actually better to use descriptive link text rather than resorting to the title attribute.

Also I'd mention you don't need alt text if the image is purely decorative - like having alt text for rounded corner images would be silly - but I've seen people assume it's needed.

Awesome on the valid code info - I wish dreamwidth did a better job with it!