During the Marvel Phase Three announcements, they set a date for a third Thor film, entitled "Thor: Ragnarok." The film will hit theaters on July 28th, 2017.
Here's where it gets a bit tricky. The word "Ragnarok" means a few things in the history of Thor. The first comes from a story line entitled "Ragnarok" from THOR #272-278. In this story, from 1978, the end of all the gods looms on the horizon Loki returns and the Midgard Serpent attacks. Thor, Sif, and the Warriors Three have to come together and stop the madness.
The second Ragnarok took place during Disassembled, where Asgard, its inhabitants, and Thor all seemingly die. The story took place in issues #80-85 during the 1998 volume of THOR.
Finally, Ragnarok appeared again in issue #3 of CIVIL WAR. Ragarok, this time, was a cyborg clone of Thor, who had all of his powers. The character was a pretty big part of the Civil War story line, so this version seems the most plausible. Maybe the real Thor has to fight the robotic Thor in the aftermath of Captain America: Civil War?
On July 28, 2017, Thor: Ragnarok hit theaters.