I have been working on some games in Silverlight. However, the community and portal support are still rudimentary at this point. While I expect it to improve over the next couple years, I don't plan to wait around for that.
I'm coming from a .Net heavy development background. What would you suggest I read and practice to start developing my games in Flash?
Essential ActionScript 3.0 by Colin Moock as clownbaby suggests. Very good book for grasping AS3 in general.
ActionScipt 3.0 Animation Making Things Move! by Keith Peters is great for more advanced topics and actual game related stuff.
Good resources:
There are plenty more excellent blogs out there these are just some off the top of my head
You may find ShineDraw really useful, as well. Terence Tsang, chooses a task or effect to do in both Flash and Silverlight and then shares the results and the code samples.
You may want to consider using Flex Developer as your primary platform for development. The Flash editor is designed more for animation. Develop your visual assets as SWFs in Flash and use Flex for your coding/development.
I found this article/tutorial pretty helpful. It's a step-by-step guide to creating an animated game with Flex. Covers double-buffering, animations, embedded resources, sound, collision, etc. Pretty good design with OO principles as well.
Flash Game Development with Flex and Actionscript - Getting Started