This installer adds ActionScript syntax colouring and a Test Movie in Flash command to the awesome TextMate editor for Mac OS X. Test Movie in Flash works with .fla files added to your project (hit Cmd-Rtn with a .fla file selected), although at the moment TextMate displays binary files as text, which for a large file can be slow. Hopefully this issue will be dealt with in the upcoming 1.0.1.
The installer adds the bundle to /Library/Application Support/TextMate/Bundles/. If you prefer to do it manually (if you want to put it in ~/Library/Application Support/TextMate/Bundles/ for example), download the bundle.
Update: the latest version of the ActionScript bundle can be checked out from the MacroMates Subversion repository.