AMFPHP is a great way to get data from Drupal via the AMFPHP module (or other PHP web apps) into Flash with a minimum of processing overhead.
As of two days ago, Adobe has announced that they will open-source their BlazeDS (formerly Adobe LiveCycle Data Services ES) server, as well as the complete specification for AMF (PDF link).
I'm impressed with the number of things that Adobe is open-sourcing as of late. This strategy is winning them the minds of multimedia developers, and it may end up with their domination of the web and desktop spaces as Flex and AIR roll onwards. I, for one, welcome our new Adobe overlords.