Earlier today Facebook announced that they have launched a full WordPress plugin. The Facebook developer blog has a full overview of the plugin which is available now from within the WordPress admin plugins page.
The plugin allows you to post directly from WordPress to your Facebook profile. The plugin also allows for Facebook comments, Facebook like button, Facebook share button along with an activity option.
To use this plugin, you need to setup your blog as an application inside of WordPress and then link up your Facebook account with the plugin if you want the full functionality of the plugin.
One important note – when I added the Facebook plugin to one of my blogs – the like button completely removed ShareThis and the Facebook commenting option completely removed the regular WordPress commenting option.