I won a copy of CSS Mastery from Andy Budd's website a couple of weeks ago, and it is excellent. It's practical and useful, in that it shows the reader how to write the most common layouts; 2-column, 3-column, fixed, liquid, elastic etc. As well showing how to do things, it also explains why things have to be done a certain way, such as differences in box models, different browser versions and so on.
I tried out one of the layouts, and it took about 15 minutes, and just worked. I understood exactly what was going on, and knew why I had to do some of the stranger things.
It seems that CSS is like chess. Before reading this book, I knew the rules, what the pieces were and how they moved. After reading the book, I feel like I know how to use the pieces together, some standard openings, and how to actually win at it. Fantastic.
There's a free sample chapter on the book's website, so you can see for yourself.