Some ( of my preferred ) useful code libraries for flash developers:

- Papervision3D ( 3D Engine )
- PaperWorld 3D ( 3D Game Engine )
- FLARToolkit ( Augmented Reality )
- TweenMax ( Tweening Engine )
- APE ( 2D Physics Engine )
- BulkLoader ( Loading Kit )

- AS3crypto* ( Security )
* Haven't got to try this yet but it sounds interesting 

Credits for this goes to Adrian Parr. Click here to view the full post on his site.