Which Enterprise Service Bus (ESB) product you evaluate and choose will depend on your exact ESB requirements, your budget, and any existing vendor relationships or products, but according to Forrester (and me), you might want to at least look at the following ESB products:
Commercial Enterprise Service Bus Products
- Software AG Webmethods Integration Server
- Tibco Active Matrix Service Bus
- Oracle Enterprise Service Bus
- Progress Software FUSE ESB
- IBM Websphere ESB
Open Source Enterprise Service Bus Products
As an aside, Spring Integration provides an easy entry into the world of ESB concepts, providing a single instance, easy to use integration container with many ESB-like features. Regardless of which ESB product you end up with, I would consider, assuming you're using Java, decoupling your code from the underlying ESB or low-level protocols using Spring Integration.