General references:
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.
Digital Web
Magazine
Lots of interesting articles listed here, though it takes a bit of digging.
Smashing Magazine
Easy-to-use tutorials, and lots of designer stuff to sink your teeth into.
Useit
Believe it or not, there is some good info at Jakob Neilsen's site on web usability.
W3C
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.