SapphireSteel has announced a few hours ago a brand new Flex / AIR plugin for Microsoft Visual Studio. The plugin will come out in two different version: Amethyst Personal (available next week) and Professional (available 2009).
Amethyst Personal is a free Flex/AIR IDE  which will provide a project management, editing, building and launching environment for Flex/AIR/ActionScript. This will be completely free and may optionally be installed into the free Visual Studio ‘shell’ edition.
Amethyst Professional will provide a drag+drop visual design environment for Flex and AIR. The visual designer will integrate with Visual Studio’s Toolbox, Property panels and code editor to provide a seamless design-and-code experience which will be familiar to C# and VB developers.
Amethyst Professional will also include full IntelliSense capabilities including code completion, code navigation and auto-expanding snippets. Amethyst Professional will provide IntelliSense both derived from pre-compiled libraries and ‘on-the-fly’ by analysing code as it is written. It will have a powerful integrated debugger to allow you to step through your code, drill-down and examine variables in a similar way to the debugger in other Visual Studio languages.