There are many framework out there in market for flex, but those who have worked on Spring framework for java would agree when I say that spring-as is a nice framework worth trying
Spring AS :
Its an IoC based framework, the base container controls, manages the creation of an object its dependency.
Benefits of using Spring AS :
1. A structured and proper dependency injection.
2. Those who work either in Cairngorm or Pure MVC can easily use this as a wrapper.
3. A run-time configuration gives a provision to decrease the need of re compilation of SWF for just configuration changes like when we deploy our application onto different context, the endpoint should be configurable without a need of re compilation.