The Microsoft patterns & practices group has just released a beta version of Application Architecture Guide 2.0 (available for download). Lonnie Wall of RDA was a contributor for this book. I knew a little bit about this as Lonnie met with Colin Murphy and me to discuss workflow. We could not resist talking about K2 but third party platforms are not part of this architecture assessment.
I have just started to read over this and now I am enticed to make time to read the whole thing. Much of the content of this will help architects and decision makers during an Elaboration phase of a project to navigate the Microsoft stack. They have guidance on how to start architecting a solution, design patterns, best practices for layers, etc. They even get down into pro and cons of using things such as ADO.net vs. Entity, when to utilize LINQ, when to use WF and BizTalk, web application design considerations, SharePoint application, etc.
It seems pretty comprehensive so far and should be used as a starting place. There are still limitations on topics discussed in this book (for instance the limitations of Excel and InfoPath services for SharePoint are not really dived into too deeply). There are probably some other similar sorts of things in the book, but from what I know the purpose of this book was to again give a starting place.