I was just introduced to two incredibly useful tools.
FlexPMD helps to improve code quality by auditing any AS3/Flex source directory and detecting common bad practices.
fxSpy allow you to inspect and dynamically change most properties and styles of the visual components in your Flex application. You can – for example – try out a specific width or a background color for your component before changing it in your code.
If you haven’t yet seen them I highly recommend checking them out.