Service-Oriented Architecture : A Field Guide to Integrating XML and Web Services by Thomas Erl, Prentice Hall, 2004.

This is a highly-recommended book on Web services and service-oriented architecture. It can help you think differently about XML. It provides you with a step-by-step guide for succeeding with Web services. It is about software engineering with new technologies and new ways of thinking.

I have put it in my library, and will spare some time to have a go on it. Here is the website of the book: SOABooks.com, which supplements the book with a variety of resources, including a complete glossary, examples, articles, and current industry information.