Off the top of my head, Facebook uses <wbr> to format link text. Eg

  <a href="http://28.media.tumblr.com/tumblr_lupq8leShl1qgxeuqo1_500.gif">
  <span>http://28.media.tumblr.com/</span>
  <wbr />
  <span class="word_break"></span>
  <span>tumblr_lupq8leShl1qgxeuqo1_500.</span>
  <wbr />
  <span class="word_break"></span>
  gif
  </a>