Starling is a free framework by Gamua built on top of the Stage3D libraries that put traditional 2D sprites on the GPU to take advantage of the hardware acceleration that Molehill gives us in Flash 11. This vastly improves performance for 2D games, and Rovio has already utilized this framework to port Angry Birds to Flash. 

Now a book is freely available at O'Reilly for download written by Thibault Imbert that will help you get started on this great framework.

http://shop.oreilly.com/product/0636920024217.do