Outside of the Flash interface, what do you guys use to edit and debug your AS3 classes in? I use Flex Builder for the brunt,but when I have no need to debug or just want in and out fast,I use notepad to view or edit.The following are some other MXML/AS3 editor or development environment.

Aptana

An integrated development environment for creating Adobe AIR^TM (formerly code-named Apollo) applications.

Intellij IDEA

IntelliJ IDEA is a commercial Java IDE by the company JetBrains.It allows programmers to quickly redesign their code.Many advanced features are supported by the IntelliJ 7.

• Smart code completion for MXML and AS files, with cross-resolution of code symbols between them, even inside of mx:Script blocks and attribute values
• Automatic code formatting, highlighting and styling
• On-the-fly code validation with instant quick-fixes
• Code insections to hunt perfomance bottlenecks, bad code practicies and other problems
• Rich set refactorings

FDT

FDT is an ActionScript plugin for Eclipse developed by Powerflasher.It provides support for AS3 and Flex development projects with syntax highlighting, code hinting, code folding and Live Error Highlighting to name a small percentage of the overall feature list.

SEPY 

SE|PY is a FREE ActionScript editor for Adobe/Macromedia Flash files.

FlashDevelop 

FlashDevelop is a .NET open source script editor designed mostly for Actionscript 2/3 development.

Spket IDE

Spket IDE is a toolkit for JavaScript and XML development.It provides support for MXML with syntax highlighting, code hinting, code folding.