I recently took a deep dive into the internals of the ASP.NET MVC code to facilitate a design discussion around web application extensibility. MVC is extremely well suited to extensible use, providing an opening at just about every step in the execution life-cycle
I created a detailed sequence diagram of the action execution path, and something of an overview of the request life-cycle. I have glossed some details - especially concerning alternate paths for asynchronous vs. synchronous execution.
I don't have a lot to add beyond the notes I took while I created a couple of sequence diagrams, but I have shared both the images and the original UML diagrams project for VS 2012 if you may find them useful. If you improve or expand upon them, please let me know. Enjoy.