The Zen of CSS Design by Dave Shea and Molly Holzschlag
It isn't often you can call a technical book lovely, but this one is. The Zen of CSS Design is one of those rare books in which every element seems to come together in perfect balance and harmony. Kind of Zen, actually. In my admittedly inexpert opinion, this is the best book on web design to come out this year. For me personally, it's been the best I've ever read. I don't know if it is the result of a random congruency of time, level of learning and need, but this book has inspired and excited me about web design more than any other.