Here are some places I go when I need to learn something new:

• W 3 Schools: when i was first learning basic html I turned to them often.  I love that they let you test what they are teaching – really helped me understand more about what I was doing.  And I still go there when I need a basic understanding of a particular technology.
• Site Point:  I have several of their books and visit thier forums fairly often.  Lots of good solid information.
• HTML Dog:  When I was working for a large Fortune 500 company I became interested in web accessibility.  At the time, our company was using a navigation system that required mouse clicks (you can’t see the mouse trail if you are visually impaired) and I wanted desperately to show my collegues that there was a better more accessible way to build navigation that still had the cool drop-down action.  I, and many others, are in debt to the developers at HTML Dog for  their “Sons of Suckerfish” tutorial
• Accessify:  I’ve only recently discovered this site, but find some the tools very helpful.
• Listomatic:  If you want some examples and code for quick navigation to here.
• Dynamic Drive CSS Library:  Great starting place for tableless builds