I agree that both
http://www.w3schools.org/ and http://www.alistapart.com/ are both excellent sites for css. w3schools has general level tutorials on almost anything you want to know about web development.
I send my students to both sites all the time.
Another great tutorial for how to do a really nice CSS rollover menu is from the project seven web site
Actually, I have a page on my site with a list of links for my students. There are tutorials to all types of web design and development things there. My site is under a major rebuild right now so a lot of the content is not accessible right now, but this page works.
Besides being a shameless plug for myself, it will save me typing all those links out.
The more time I save by not planning and documenting,
the more time I have left to debug.
There's some pretty useful stuff at
a nice way to learn superb css is downloading some css-files from:
And when you're up to it create one yourself...