I'm one who still likes propping open a book as I learn stuff. This is a really good question. Right now there are a lot of books on advanced CSS techniques (like CSS Secrets, as Robert says - and it's a great book) and articles and tutorials on fancy edge case stuff, but what should a dev wanting a practical understanding of CSS read now? My call would be Jump Start CSS by Louis Lazaris. It's about the best recent book that gives the basics and then a bit more. Disclaimer: I worked at SitePoint when this came out - still a good book.