Intellij 8 - alternative to FlexBuilder
If you've ever used IntelliJ for java development, are frustrated with eclipse, or you wish Flex Builder could do more (and you never use design view). This might interest you.
JetBrains has added Flex development support to IntelliJ 8. Which was just release (nov 6th). Note, they have only added code support with no plans for a UI designer.
http://www.jetbrains.com/idea/
Some of my favorite features
1. CODE FORMATTING!!
cntrl-shit-L and boom the as/mxml file is formatted to my liking.
2. Flaging common errors without running the compiler.
3. Navigating between classes and around a class.
you can jump from an interface to the as classes that implemented a given menu.
4. CNTRL-Q help
Put your cursor on a method or class and hit cntrl-q, intelliJ will dynamically pull the comments out of the code for that class/method and show it to you as help
5. Code generation
It's easy to auto generate get/set method for properties, constructors, implemented methods, override methods
6. Find Usages
A quick search of all the code that uses a given variable to method.

is integrated into the Flex Module for flex applications and libraries (no AIR support).