How to remove the "Be the first of your friends to like this" part of the standard iframe Facebook Like button?

IMO the easiest way is to resize the generated iframe with CSS to 54px width (small button). Unfortunately, the iframe doesn't has a class or ID, but you can match it by src attribute:

iframe[src*="://www.facebook.com/plugins/like.php?"]

Of course matching it with a descendant selector is easier.