We are currently working on a MVCS implementation in the Spring ActionScript framework. It uses the full power of the Inversion of Control container so you have centralized dependency management and are able to swap things easily. It is not very prescriptive in how you do things but provides you with a very flexible infrastructure.
If you are new to Spring ActionScript and MVCS, I have an introductory post at my blog: http://www.herrodius.com/blog/158
