Some places where you can discuss ActionScript, especially for game development
Flash Game License - Code Talk - first as it's where I hang out most, as well as other forums on their site related to particular APIs.
Mochi Community - another fairly professional community though fewer code related discussions.
Kongregate - Game Programming forum - the only other place I sometimes hang out (my account there is JWBSoftware for historic reasons). Too many newbies but best for discussions on their API, for which there's a dedicated forum.
Newgrounds - I'm registered there but never join in. As with all sites with lots of game players the proportion of newbies is too high.
ActionScript.org - ActionScript 3 forum - I don't know much about this site but looks at least as busy as the others.
Adobe Forums: Action Script 3 - for completeness though I never use it as I find their interface horrible; I've used other forums there for tech support.
There are many more game related sites, but all I've seen have much smaller programming communities or Flash and ActionScript is just one of many things discussed. Let me know of any I've missed.