This is an updated version of the instructions originally provided by user jcryle here. The modified step appears in italic.
► Follow these short, easy directions to set it up on your blog:
1) Your Dashboard
4) Under “Available Services” click “Add a new service”
5) For “Service Name”, type in Facebook
6) For “Sharing URL”, copy this link ► http://www.facebook.com/sharer.php?u=%post_url%
7) For “Icon URL”, copy this link ► http://cdn.iconfinder.net/data/icons/Classy_Social_Media_Icons/16/facebook.png
8) Click the “Create Share” button
9) Drag and drop your Facebook SHARE button to either the “Enabled Services” section below the “Available Services” OR over to the right with the WordPress SHARE button.
10) Near the bottom, in the Button Style drop-down menu, select “Official buttons”, save everything at the bottom of the page and you’re all set.
You now have both the SHARE and LIKE options available to you at the bottom of your posts.