It's bad enough that I never understood why the US Department of Health and Human Resources produces such a useful site about user centered design, but now I've discovered that the Australian Government has gone and done the same thing.
For usable web design, the US site, Usability.gov is a fantastic resource. They cover accessibility, traffic log analysis, market research, usability guidelines, web design checklists, and more.
In Australia, you can find the same in the Australian Government Information Management Office's Best Practices section.
Their Better Practice #15 Information Architecture for Websites is a real gem. They offer checklists on navigation, user testing, implementing website search and information architecture.
Though offered by government entities, any Webmaster can find valuable help at these web sites. If you're learning the basics, or refining web site guidelines and standards, these two web sites offer a wealth of knowledge, and are easy to use as well.