Alternative to Polling. HTML Updates

I am working on a collaborative website that I want to give users notifications while they are viewing or editing data. Something similar to how in StackOverflow if you are replying to a question and the notification at the top pops up saying that there is a new reply to the post.

I can see how to do this using some kind of polling AJAX magic, but I was wondering if there was any way to push the notification to the browser w/o using polling?

Thanks for any help/ideas :)

EDIT:

For those interested, I went with SignalR https://github.com/SignalR/SignalR/wiki/Hubs