Having just finished reading David Flanagan's "Javascript: The Definitive Guide" (5th edition), I've found that it's got the best explanation I've ever seen of the core functionality of a language. He explains everything, from identifiers and expressions on up, so clearly that it's easy to visualize how every part of the language works.
I want to move on to a good CSS book now; I've learned a fair amount of CSS over the years, picked up in bits and pieces, but I'm looking for a good from-the-ground-up CSS book, akin to the aforementioned Javascript book.