I don't know the people who run this site, they aren't paying me anything to pimp them, but if you have not checked it out, you really should. The name is www.devmaster.net. Felixters from "the kit" (www.flashkit.com) sent me a link to a wonderful article on OOP game design, and it happened to come from this site. After a thorough perusal of the site's contents, I give it a high rating. The forums don't have a very large Flash presence, and in some cases they are actually a little ill informed about the complexity of making a game in Actionscript (like many game dev forums), but there is a wealth of content on general game design, especially the link above.
Some other great tutorials and articles that might interest the Flash game developer:
An introduction to pathfinding
An introduction to finite state machines
Physics Based BSP Trees: Collision Detection
Using trees for Sorted rendering
The Basics of Raytracing
Software rendering School Part 1
Lua Scripting 101: The Basics
There are more, and the forums are filled with interesting discussions. Since they have little knowledge of Flash and Actionscript, I wouldn't go looking for specific Flash answers as there are ample existing forums for that (flashkit, Kirupa, actionscript.org, and more).