Old Man Logan is considered to be one of the best Wolverine stories ever written. This is particularly interesting because, in the long run, it is not that old. However, in its short time in existence, it has stood as a story that examines the character of Wolverine in a way that few other stories can.
For those of you who are unaware, Old Man Logan tells the story of Logan living in a post apocalyptic world, where the super villains have won. Almost all of the heroes have been killed, and the villains have divided the world amongst themselves, with the Red Skull acting as their (kind-of) leader.
According to recent reports, this is the story that Fox wants to adapt to the big screen for Wolverine 3. As you can tell from the above description though, this will be difficult. Fox does not own many of the primary players of this story, so whatever happens, it will be quite different from the comics.
The one benefit to this though, is that Mark Millar wrote Old Man Logan and Millar is currently working for Fox as an advisor for the X-Men and Fantastic Four films. If anyone could help make changes to this story, while keeping it true to its roots, it would be him.