I've recently had the opportunity to look over a yet-to-be-published book from Manning titled "Open Source ESBs in Action". If you're an ESB user, you owe it to yourself to check this one out as soon as it's available.
In an unusual twist, the authors of this book presented ESB best practices and techniques using *two* open source ESBs, Mule and ServiceMix. I'm already a Mule user, so I was pretty happy to see several new ideas to employ in my Mule use. I haven't tried ServiceMix yet, but may someday, time allowing. (I'm confident I can run several scenarios right out of the box, armed with this book.) The authors cover more than a few patterns straight out of "Patterns of Enterprise Integration". Kudos to Manning for allowing their authors to acknowledge this excellent resource, even if it comes from a different publisher. I really do appreciate that!
I liked several ideas I think I'll apply somewhere down the line-- including use of XML on Mule to facilitate validation and transformation, use of JibX to help make object-to-XML transformations, and use of a BPM product to oversee non-integration parts of my ESB. (I suspect that'll de-tangle the configuration a great deal, or at least make it easier to understand.)
By using two ESBs to implement every use case, I think the authors give you some insights you might otherwise have missed if you saw just one side of the story. As I said previously, unusual, but interesting.
I won't go on and on-- let's just suffice it to say this book will have a spot on my bookshelf when it becomes available in the near future. If you use an ESB, or think you might like to, you might consider looking at this informative work.