For a limited time, Sitepoint is giving away for download a free copy of The Art & Science of CSS. We have used this book to organize a few meetings over the past couple of years. It is an intermediate level work that covers specific aspects of a web page and shows how to style each in different ways.
Sitepoint actually calls this a Twitaway, i.e., a Twitter giveaway, but it is not necessary to use Twitter to take advantage of the promotion. Full instructions and more information are at this page of the Sitepoint website.