I have been scratching my head alot these days over design and architecture for an Enterprise Service Bus. Sometimes I tend to drift towards "Just A Message Bus", other times I think about "Message Queues" and then there is a whole world rushing towards ESB. I believe I am going to write small and precise comparison and contrasts on which one to go for.
But for now I will suggest you to have look at this following article that I came across @ MSDN.
Microsoft on the Enterprise Service Bus (ESB)
Surprisingly, Microsoft hasnt published a lot of text on Message Buses and Enterprise Service Bus, their flagship product is BizTalk when it comes to integration and broker scenarios. However I came across a lot of good articles and Red-Books published by IBM that targets and focuses on ESBs and SOA etc.