One of the more exciting things going on in the Microsoft development world is the upcoming release of Silverlight.  Silverlight is (or soon will be) Microsoft's answer to Adobe's Flash and Flex products.  Silverlight technology is powered by the .NET framework in the form of a trimmed-down CLR (CoreCLR) that runs on both Windows and Mac -- Scott Hanselman has a pretty good summary of the product and its associated jargon here.
Based on the early examples, I think Silverlight will quickly achieve the ubiquity that Flash has enjoyed; hopefully it will stir the interest of .NET developers who have avoided Flash in the past and drive the development of some really useful applications.  There's also a good DotNetRocks podcast available in which Brad Abrams discusses the philosophy behind Silverlight and gives some glimpses of its future direction.