This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread 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.