ASP.NET 4.5 now includes support for HTML5 Web Sockets which can provide a great way to add real-time communication to a Web app where a server can actually push data live to one or more clients. In this video from the New Features in ASP.NET 4.5 Pluralsight course I walk through getting started with creating a Web Sockets server using a Nuget package from Microsoft called Microsoft.WebSockets.
Learn to Use ASP.NET 4.5 Web Sockets - The Easy Way
If you'd like to learn more about the new features in the 4.5 release and in Visual Studio 2012 check out my Pluralsight course.
Download samples of using the "raw" ASP.NET support for Web Sockets as well as the Microsoft.WebSockets support here. I've also included a Node.js sample for anyone who may be interested.