If you would like to add a Facebook plugin to your site there are several tools available. These are not WordPress plugins but plugins that Facebook has developed that allow you to simply copy and paste code into your site to add their functionality.
One of the more popular plugins is the Like plugin (see below) that you find on most websites in the sidebar. If you are active with Facebook, this is a good way to tie your site with your Facebook account.
To view all the plugins that Facebook offers, visit their developers page for more choices and options: