A List Apart
A nice collection of articles on many key issues in web design -- some from the presentationalist side, but generally more balanced in approach.
Lots of interesting articles listed here, though it takes a bit of digging.
Easy-to-use tutorials, and lots of designer stuff to sink your teeth into.
Believe it or not, there is some good info at Jakob Neilsen's site on web usability.
The World Wide Web Consortium -- the folks deciding on web standards. A fairly technical site.
WAI - accessibility
Part of the World Wide Web Consortium -- leading the charge on accessibility.