The following is what we know so far. As always details are subject to change as a the film is in early stages of production.
Thor 3 confirmed. source
Craig Kyle and Christopher Yos have been hired to work on the script. Craig also did production work on the original and its sequel. source
Thor 3: Ragnarok is a rumored title, but this is likely too early to take seriously. It makes sense that they would go for the Norse Armageddon scenario to close out the trilogy, but that is just conjecture. source
From the same source we have news of a Agents of S.H.I.E.L.D. tie in. Since AoS have been favoring Asgard references I think this is extremely likely.
Speculation is that the movie will premiere in May of 2016 to compete with Batman Vs. Superman. source
Will update as more details emerge