There are no details yet, but SapphireSteel Software is planning to release an IDE for Adobe Flex and AIR that integrates into Microsoft Visual Studio. Here's what I've heard from Huw Collingbourne:
I thought you might like to get advance word on our new product which is called Amethyst. This is not a Ruby/Rails product this time – in fact, it’s for Adobe Flex/AIR. That said, it can integrate with Ruby In Steel to create a multi-language Visual Studio solution with Flex at the front end (the view) and Rails at the back end. We won’t officially be announcing details of Amethyst until next week but we are now so close that there is no embargo on this.
Initially, we are releasing a free Personal Edition of Amethyst, which will provide ActionScript and MXML editing plus project management hosted either in a commercial edition of Visual Studio or the free Shell edition. We are launching the first public beta of Amethyst Personal Edition next week. Later on (in the 2nd quarter of 2009) we will launch a commercial Professional Edition - which will have a drag-and-drop Flex/AIR visual design environment, IntelliSense and graphical debugging tools all seamlessly integrated into Visual Studio.
I'm intrigued. There are times that I wish that Adobe FlexBuilder had an integration with Visual Studio in addition to Eclipse, but I feel like that might be unusual. Of course, I'd want the version with the IntelliSense support and the graphical debugging tools.