Facebook Open Graph META Tags
Although I have used the FB Open Graph META tags before, more so when sharing URL's of everything I have developed, the META tags came in useful when I wanted a personalised description and image to appear on my FB wall.
What I did not know was that these META tags also effected the "LIKE" feature, where the site I am working on at the moment when liked just scraped what it could and displayed it, which the client was not a big fan of. Something to bear in mind I guess.
More can be found here: https://developers.facebook.com/docs/share/