Publish / Subscribe with WCF
I'm working on a series of articles about building an ESB on your own.
http://www.iserviceoriented.com/blog/post/Building+Our+Own+ESB+-+Publish+Subscribe+Part+1.aspx
http://www.iserviceoriented.com/blog/post/Building+Our+Own+ESB+-+Publish+Subscribe+Part+2.aspx
http://www.iserviceoriented.com/blog/post/Building+Our+Own+ESB+-+Publish+Subscribe+Part+3.aspx
When at the end of each group of articles, I'll be providing downloadable source code to play with. Keep in mind this is simply to teach some concepts like message queueing, building extensible systems, and WCF. Though you are free to use any of the sample code, it is sample code, not a fully tested and supported product. If you want a great fully functional ESB, I highly recommend checking out Neuron. Anything Sam works on is gaurenteed to kick ass.