I use Aptana plugin to write Flash/Flex/AIR in Eclipse. For AIR in particular, Aptana's AIR app launcher is great. However, one key component missing from Aptana is ActionScript 3 (aka AS3) editor. I've been limping along by mapping .as files to Java editor but I just remembered an old Eclipse plugin that used a template to control syntax coloring. So I went looking and found it here: color editor. It was still being maintained. Woot.
It comes with AS2 support but not AS3 so I went searching again and found the mode file for AS3 here: actionscript 3 syntax hilighting for jEdit. The color editor reuses jEdit's syntax coloring mode files. Almost there.
I expanded the color editor jar file into Eclipse 3.2 plugins directory then dropped the jEdit AS3 module ("actionscript.xml" file) into it's 'modes' directory. Restart Eclipse and used Open With to open some .as files. Eeeks. Too colorful to say the least. The color editor came with color preference settings panel so I changed the colors approximately match that of Java colors. Better.
Then I noticed that some keywords were missing (new, delete, super, etc.) so I added them to the actionscript.xml file and went back to coding. Note that Color Editor doesn't fully understand AS3, just enough to add some colors which I find useful.
BTW, TextMate Bundle for AS3 can be found in TextMate code repository.