Just ahead of this year's Comic Con, Marvel Studios have announced release slots for five more films which takes them though to May 2019.
Here's their full schedule as it currently stands. The specific titles haven't been announced yet aside from "Doctor Strange" which seems almost a certainty to take the July 8th 2016 release date slot. It's hoped at least one or two of these TBD films will be announced at Comic Con next weekend:
August 1st 2014: "Guardians of the Galaxy"
May 1st 2015: "Avengers: Age of Ultron"
July 17th 2015: "Ant-Man"
May 6th 2016: "Captain America 3"
July 8th 2016: TBD (likely "Doctor Strange")
May 5th 2017: TBD
July 28th 2017: TBD
November 3rd 2017: TBD
July 6th 2018: TBD
November 2nd 2018: TBD
May 3rd 2019: TBD
Speculation is already rife. Of the six unknowns there are three essentially guaranteed titles already - "Thor 3," "Guardians of the Galaxy 2" and "The Avengers 3". At least two of the others are expected to be non-sequels. Those could be a variety of titles including Black Panther, Inhumans, Ms. Marvel, Nova or a standalone Black Widow movie.
The biggest surprise is 2017. Instead of a dual release, the studio is opening three films that year, and then is opting out of the early May release slot the studio has occupied since the first "Iron Man".
Could that nine month gap be a breather between Phases 3 & 4? If so that would almost certainly mean 2017 is Thor 3/Guardians 2/Avengers 3 whilst 2018 onwards is essentially open as various contracts are up. Might one of these last dates be a post-Downey "Iron Man" standalone?
The most logical theory is "Avengers 3" is the May 2019 release which would indicate Phase 3 is considerably longer than its predecessors.
Source: Marvel Studios