I just read XSS Attacks by Jeremiah Grossman, Robert Hansen, Anton Rager, Petko Petkov and Seth Fogie. The book is a comprehensive analysis of XSS and related vulnerabilities, and covers everything from a beginner's introduction to XSS through to advanced exploitation and the latest attack techniques.
Overall, the book is well-organised, technically accurate, and full of pertinent examples and code extracts to illustrate the different vulnerabilities and attacks being described. There are plenty of tricks that will benefit even experienced web app hackers, including a wealth of filter bypasses, and coverage of offbeat topics such as injection into style sheets and use of non-standard content encoding.
Here and there, the book displays the effects of multiple authorship, notably in the discussion of the best tools for finding XSS flaws. I know that some of the authors have rather opposing views on that question, but it is always good to get different people's perspectives on the tools they find most useful. There are also a few typos and editorial glitches, but that is the price you pay for being quick to market, as they evidently are.
Overall, this is a great book that will benefit a wide range of people, from novices to seasoned hackers. It is fun to read, with plenty of lighter moments punctuating the technical meat. Nothing else currently available is hitting this target - get it while it's hot!