Microsoft ESB Guidance up on CodePlex...
The Microsoft ESB Guidance, Co-authored by Neudesic and released back in December 2006 in a "partner only" set of bits, VPC, documents, has been released to the public up on CodePlex
http://www.codeplex.com/esb
This is CTP code with lot's of good patterns and concepts that I was fortunate enough to use as "inspiration" on a project I worked on several months back while at Avanade / Accenture. Certaintlyl allowed re-use of a patterns for concepts that made it into working code.
Take a look, if not for the free code, for the patterns and concepts.
To take it to the next level, take a look at Neudesic's ESB product; Microsoft platform based, but not bound to BizTalk with support for a variety of transports such as MQ Series, Peer to Peer (for low latency), etc. Built upon Windows Communication Foundation (WCF) extensible architecture.