ASP.NET MVC
Home -
http://www.asp.net/mvc/
If you're familiar with design patterns, MVC (Model/View/Controller) should be no news to you. If you're familiar with django, ruby on rails, jboss seam or any other web framework that follow the MVC pattern, you'll find this quite interesting as it was solely based on those frameworks and tends to learn from their mistakes.
If you already use ASP.NET, this is the way to go.
If you're planning on going the RESTful awy, this is the way to go.