I like http://www.only4gurus.com! Not only for the many videos that are downloadable, but also for the great content that is available. Today I got notification of this useful article that will interest some of my co-workers (if they are not too focused these days on SharePoint :-))
The BizTalk Server pipeline architecture opens up a wealth of opportunities by allowing you to plug in you own components. Technically, when developing so called "custom pipeline components", only a few basic principles need to be taken into account. As such, nearly any .NET developer should be able to get away with it within a few hours.
In order to even further improve this developer experience, this article aims at explaining and introducing a couple of basic principles and techniques.