A very good book containing a lot of tips and tricks from various departments, starting at beautifying design and ending at improving usability and accessibility. It's compiled in very user-friendly format of questions and answers with full source code. It is, however, targeted at CSS novices - or it used to be an overwhelming compendium five years ago, when CSS was still new.
SitePoint has recently released 3rd edition of this book (I have 1st) - but I've read its info and it looks like it was updated with revised source codes and tricks for IE7/IE8 and FF3. It's quite misleading now to label such a book as "101 Essential Tips, Tricks and Hacks" because it implies more advanced approach than what CSS Anthology really contains. It's a good book for beginners, but not worth the money for advanced users.