Code contest: how to horizontally and vertically center that div?

You've seen so many implementations, but is there a best way? Comment your way to stardom with your best implementation. And if you don't understand what I mean, then check out the other's and you'll gain some insight into the crazy world of web development. (It should be simple, right?)

Use whatever strategy you like - but posting an example in jsFiddle or Codepen would make you that much cooler.