If there's a book to use when introducing someone to the ideas of usability on the Web, I'd have to say that I think this is it. Not Nielsen, and not Cooper (at least not to start with). Steve Krug's "Don't Make Me Think" has the most no-nonsense and easy-to-follow approach I think I've ever seen, and best of all, he makes SENSE.
First of all, Krug deconstructs some of the sites we all know and use often, and he does so to help us see what we should be doing, as well as what we should not. I remember being especially impressed with his in-depth analysis of Amazon.com's navigation scheme (Chapter 6 - "Street Signs and Breadcrumbs"), from the use of tabs to the structure of the sub-navigation to color changes, he covers it all with a sense of humor, clear pictorial examples, a sharp eye for detail, and a clear concise explanation of what works and why. The reader is left with a greater understanding of not only why Amazon has been so successful, but also what choices they made that helped them find this solution.
The chapter on usability testing (Chapter 9 - "Usability Testing on 10 cents a day") was another fine example of clear communication and great ideas. Krug's breakdown of how the usability process should be conducted, and why it's needed in the first place, is concise and not preachy, as some usability authors are, and it really gives the reader an excellent idea of how they can fit usability into their process. This is probably the best way to "sell" usability to someone, and he does a great job of it.
The whole book is like that, really, but those chapters were highlights in the book for me. His ideas on simplicity of presentation and home page design were also well-taken, both as a designer and as someone who uses the web. Perhaps that is what makes his book so excellent, is that really, anyone could get something out of it. Whether it's the person who surfs the web now and again or the one who designs the pages for it or the one who's paying for the person to design pages for it, anyone could read this book and benefit from it, without having to wade through piles of needless verbage or proselytizing.
In the end, "Don't Make Me Think" seems to be an example of what it advises... it keeps things simple and accessible for a wide variety of people, and thereby makes itself useful as an excellent resource. The next time someone asks me what Web usability is all about, this is the first book I'll be recommending to them.