Microsoft have got a free eBook that can be downloaded that looks at Service Orientated Architecture(SOA).  An cursory look at the book suggests that it is pretty comprehensive.  But more importantly is very pragmatic, and from the outset identifies that SOA is an architectural concept rather than a specific set of technologies – a common misconeption. Although technologies such as web services and Enterprise Service Buses (ESBs) are often used as means to release an SOA architecture. 

Book examines a range of issues including:

• Basic SOA tenets
• Service Lifecycle
• Workflow
• Data Management and how article styles may impact upon the data

The book can be retrieved from Download SOA in the Real World in word 2008 or PDF formats.  There doesn’t appear to be a treeware version of the book.