You have seen them on other sites, we even have one here on my About page. And there several different plugins that will allow you to share your page, show your likes, etc, etc. Facebook even has their own plugin with a bunch of options including auto-posting. Over on the Social Media Examiner blog they have a great tutorial to walk you through the steps in setting it up.
But if you want to add a Facebook like box that shows your fans and streams, like the one to the right, without adding a plugin, this video will show you where to find it on your Facebook page and how to set it up as a sidebar widget.