This email from Original Penguin has a nice implementation of ‘two click’ Facebook Like functionality. Clicking on the ‘like’ button in the email drives to a landing page with a similar design, which includes a working like button. Users can then use that to like the deal, posting a link to the landing page on their Facebook profile.
Unfortunately, as the integration supplied by Facebook is largely javascript, the ‘like’ action can’t actually happen in email, so marketers have to drive to a landing page and then encourage clicks there.