Update: If you're looking for the documentation of the AS3 and Flex APIs, you can find it here: http://livedocs.macromedia.com/flex/3/langref/.
In the past few days, two important resources have been released for those interested in ActionScript 3.
The first resource is the AS3 Language Specification. This is a highly detailed document showing the innards of how AS3 works. It should explain anything you need to know about AS3. And if you're a language geek and want to know things like the name for the expression of types of an instance*, then this is for you.
The other resource is the AS3 libraries released by the Adobe Developer Relations team. These are seven free ActionScript 3.0 APIs for your own hacking. If I had the time right now, I'd love to be doing some amusing things with these APIs, like keyword searching on Odeo and Flickr together, showing a gallery of images that match the keyword when the podcast is playing. I hope others can amuse themselves with these APIs (and share the results, please!)
*they're called traits