I have been looking into frameworks for Flex recently - you will find tons of blog posts around the frameworks out there.

The most useful post I have found thusfar can be found at the Adobe Developer Connection site - http://www.adobe.com/devnet/flex/articles/flex_framework.html

The article outlines the most popular frameworks available currently i.e.
- Cairngorm
- Mate
- PureMVC
- Swiz

Personally I am stuck between Swiz and Mate - I am going to go with Mate first though because it has more documentation then Swiz.

I will let you know what I think once I have given it a go.