If you know Tables based design the Jeffery Zeldman's classic "Designing with Web Standards" is a must.
"Head first HTML, with XHTML and CSS" is a good book for the basics.
Then move on to:
"CSS Mastery" by Andy Budd
"Bulletproof Web Design" by Dan Cederholm
Boagworld has a great podcast on web design and the forum is a really good resource.
Finally, Linda.com tutorials are great.