HTML/CSS is a must to know. Like mentioned W3Schools is excellent resource, also http://tizag.com/
Also some helpful "cheat sheets" found here, http://www.addedbytes.com/cheat-sheets/css-cheat-sheet/
(that one is the CSS cheat sheet, more listed on the right).
I'm not really sure what books there are to suggest, if you just get some good CSS/Html/PHP books that would be a good start.
Ya I'm not sure what books to recommend, they won't be up to date for very long. Best to just look for tutorials on the web I suppose.