For good introductoy books on SOA, I'm fond of "the green book" which is "Web Services and Service Oriented Architectures: The Manager's Guide" by Barry. It is also popular so a good common source of reference. Organized into a series of relatively short stand-alone essays - makes good source material for high-level presentation on SOA. However, the material is too high-level and too oriented on trying to convince the reader of the virtues of SOA - a bit short on the fundamentals, "nuts and bolts", of the topic. Still, provides adequate introduction to the vocabulary, issues, etc.
"Enterprise SOA: Service-Oriented Architecture Best Practices" by Krafzig et al. is a bit longer than Barry's book but still a good introductory read. It is, I believe, a relatively popular textbook for professional courses in the area. I found the case studies at the end of the book informative. Less trying to sell the reader on SOA and more informative on the benefits/risks - which is also good. Focuses on the material supporting develoing SOA-based projects - which is fine and fits the experience of the authors - but neglects some important life-cycle/TCO issues such as deprecation and retirement of services.