A new Redbook has been published called "
Implementing and Testing SOA on IBM System z: A Real Customer Case".
The Redbook does a good job of breaking down SOA implementation into a series of logical decisions, with real world implications. It covers not only the overall architecture, but the steps to get there. The final solution includes much of the WebSphere Business Process Modeling stack, including WebSphere Application Server, WebSphere Process Server, and WebSphere Portal, as well as tooling from WebSphere Integration Developer and WebSphere Business Modeler.
In particular, the Redbook shows how the SOA solutions fit into the existing ecosystem at the customer shop. SOA is evolutionary, not rip-and-replace. A good read.