FlexPMD is a tool that helps to improve code quality by auditing any AS3/Flex source directory and detecting common bad practices, such as unused/Inefficient/Over-complex/Over-long code and incorrect use of the Flex component lifecycle (commitProperties, etc.)
In the last few days I fiddled with it and with it's fairly new eclipse plugin, and found it quite useful.
The plugin also includes a CPD (Copy & Paste Detector) tool, that can identify code duplication which can be reduced by using functions or inheritance. I must admit I was overwhelmed by the amount of suspected code duplication it found in our code.
Another cool feature is the "Monitor" mode, where it only alerts of violations in files as you modify them.