ASP.NET MVC Framework
Scott Guthrie wrote excelent 1. part of his tutorial (with lot of pictures and how-to's) about MVC as a optional feature that ASP.NET will support.
This is important because it provides a structured model that enforces a clear separation of concerns within applications, and makes it easier to unit test code. It also helps provide more control over the URLs that are published in applications, and can optionally provide more control over the HTML that is emitted from them.
More info: http://weblogs.asp.net/scottgu/archive/2007/11/13/asp-net-mvc-framework-part-1.aspx