This week's book giveaways are in the Refactoring and Agile forums. We're giving away four copies each of Re-engineering Legacy Software and Docker in Action and have the authors on-line! See this thread and this one for details.
The major alternatives are commercial products such as webMethods and Tibco. Chapter 2 covers some of the open source alternatives such as Camel, ServiceMix, OpenESB, and J2EE. There are compared in terms of ease of use, maintainability, and extensibility. I have found Spring Integration to be most intuitive integration solution.