Since the day-one of the launch of MX2004 the only feature which I had been excited about was JSFL. I have been closely watching the Flash Community for new JSFL's and tools. The first of which I came across was the auto-save and mass compilation tools.
The one which is most intersting and has almost all the API's listed is the "Flash MX 2004 JSFL Reference" available at Dynamicflash and the next is the FlashGuru's "JSFL - Hidden Methods/Properties" found here.
This one looks real promising and I hope will change the way Flash can work for us. Great stuff by Macromedia guys on this part.