Don't watch the video above if you're anti-spoilers. In it, Robert Kirkman makes a joke about a main character death from The Walking Dead comic books that they've been hinting at all of Season 5. Also, Josh McDermitt (Eugene) is pretty funny.
GRRM's initial pitch for Game of Thrones has been unearthed, and in it he invisions a very different story of Westeros. It's worth noting that the story was originally to be a trilogy, during which three conflicts would occur: the Starks challenging the Lannisters, a Dothraki invasion led by Daenerys, and the Night's Watch battling with the Others. Martin has clearly strayed from this outline, as we're now awaiting book six, so hopefully many of the things he details in this letter don't come to pass. Warning: if you're afraid of potential spoilers or some real weird feelings about what could have been, quit reading now.
According to the letter, five characters were always supposed to live: Tyrion Lannister, Daenerys Targaryen, Arya Stark, Bran Stark, and Jon Snow. But what was supposed to happen to them was vastly different. In this early version, Ned Stark dies as he did in the version we know, but helps Arya and Catelyn escape to Winterfell before Joffrey kills him. From there, the two women and the crippled Bran travel to the wall seeking refuge with Jon and Benjen, where ARYA FALLS IN LOVE WITH JON. Their romantic tension was meant to be central to the story, and would have tormented them both "until the secret of Jon's true parentage is finally revealed in the last book." The Night's Watch refuses help to the Starks, so they head farther North and encounter Mance Rayder and the Others. All but Catelyn were to have survived these enounters by way of Arya's sword and Bran's magic, but what happens to them afterwards is not included. Meanwhile, Daenerys was to have revenge-murdered Khal Drogo for her brother, and accidentally stumbled upon the dragon eggs which she uses to "bend the Dothraki to her will" and invade the Seven Kingdoms. Tyrion murders Joffrey, only to see him replaced by Jaime. Somehow, Tyrion would have ended up exiled and on the side of the Starks, where he too would have fallen in love with Arya. Apparently, she would have not reciprocated his feelings, but that wouldn't have stopped a "deadly rivalry" between Tyrion and Jon.
The final paragraph of Martin's letter is redacted, presumably because it's dark and/or full of spoilers. You can see all but that last paragraph here if you want to read it for yourself. If you want to see it IRL, you can find it at the HarperCollins office in London.