How To Implement ReverseAJAX (Comet) in ASP.Net MVC
The paid alternative
There are great comments about the question in this thread.
And based in the fact you can use handlers in a MVC app:
will do the work : )
I doubt you will find something out of the box for MVC but you can always implement the client side code that handles timeouts and reconnects to an AJAX-enabled WCF service that polls for whatever event you want to be notified for. Be sure to set the timeout of the service to a higher value.
Edit 24.11.2013Since the original question was posted SignalR was released which is a library to do just that.