Good HTML references are really hard to come by, either they are just listings, like W3schools.com or terribly outdated.
Sitepoint have done quite a good job in listing all the HTML elements and categorizing them into different use cases. There is also a list of deprecated elements and attributes to avoid (which could be considered dangerous to still bring up as some of them are too handy to simply add to solve an issue) and a Microformats primer.
I am working with other portals/article sites on similar projects and hope this will help flush old and outdated tutorials out of the search engine result pages.
The reference also gives a legend of browser support, something that so so far was only available on the German SelfHTML reference.