I came across this great list of usability rules in a presentation by Denise Stephen called "Enabled by Design meets Scripting Enabled" which was given as part of the Scripting Enabled event organized by Christian Heilmann. Here goes the list:

Usability - The golden rules

• Simply presented information
• Content reduced to essentials
• Manageable logical structure
• Intuitive usability
• Uniform appearance, consistently designed
• Good design and appealing graphics
• Quick delivery of information

There are some great slides at ScriptingEnabled which are up on Slideshare - like this one Why I hate the Interweb (a presentation on the challenges that face different kinds of disabled users online). View more on Scripting Enabled website.