Ben Ward: Understand the Web
What 'the web' actually is, and why building desktop-class applications on it is not what it was built for.
Keryx (X)HTML Elements Best Practice Sheet
Detailed to the point of being almost unreadable!
CSS3 Support in Today's Browsers
A table of who supports what.
Andy Budd: Blogography: CSS/Web Standards Links
A huge and valuable collection.