Here’s a good link describing some of the different plugins for the fb like button (or how to add it yourself). If have added many fb buttons, but I wanted something really quick and dirty last night (hey-o!) and went with Facebook Like Button Plugin. However, the dark scheme did not appear when I selected it and the Like box is also difficult to style. But that has nothing to do with the plugin. I will probably end up adding the buttons myself. But it was fast way to add them in 5 min.

http://mashable.com/2010/05/07/wordpress-facebook-like-buttons/

Enjoy!!