If, as I recently did, you were to buy Molly Holzschlag's outstanding "Special Edition Using HTML and XHTML" and "Eric Meyer on CSS: Mastering the Language of Web Design," you might wonder if you had awoken on some strange planet in which pricey web books were actually worth the money, and tech authors wrote at a level that both challenged, elucidated, and entertained.
Molly Holzschlag's book, simply put, succeeds on every possible level. The style is clear and personable and the information is cogently and logically presented. As a web standards "insider," she gives you the history behind the development of markup languages rather than just throwing out the standard grid of what breaks in which browsers -- because, as this book so clearly demonstrates, the "why" matters a great deal, and you can't really get your mind around that without a few little history lessons along the way.
But it is not just a collection of dry facts and background info; the book is hands-on all the way, and constantly uses work-along examples to teach how to use XHTML to author web pages.
As Holzschlag states in the intro, the perfect reader for this book is the intermediate user -- someone who has used HTML before, and is quite familiar with web authoring, but maybe wishes to finally learn to do things the "right way," now that the W3C has made some headway with specifications. The book hits its intended audience mark dead on. The info is not dumbed down, yet important concepts are explained in detail. If you encounter a concept that is over your head, chances are there will be a sidebar link to the W3C website for additional information you need to catch up. This seems to me a very good compromise between leaving seasoned professionals bored, and lower-level intermediates in the dust.
There are several excellent reference charts (such as for ASCII symbols, character sets), and a comprehensive XHTML tag reference, making this a perfect all-around desk reference as well as a tool for getting up to speed on XHTML.
I believe this book would be particularly useful for the web designer wishing to move towards using XHTML for content and CSS for style and layout. In that case, I suggest "Eric Meyer on CSS: Mastering the Language of Web Design" as a companion volume to round out the CSS side of things (Actually, Holzschlag herself references Meyer's book several times).
If you really want to make the switch to cleaner markup, and prepare yourself for what's coming on the web (and if you don't think you want to, this book might also convince you why you *should* want to...) you could hardly do better than this book.