Warning! This story contains MAJOR SPOILERS!
Just as James Gunn directed the Guardians of the Galaxy post-credit scene for Thor: The Dark World, it has now been confirmed that director Joss Whedon has directed a Captain America: The Winter Soldier post-credit scene that introduces three new characters and ties directly into Avengers: Age of Ultron. Stop reading now if you don't want to know any more.
The scene in question features Baron Von Strucker (Thomas Kretschmann), who is hiding in his underground laboratory after the fall of S.H.I.E.L.D. and HYDRA, where his men have Loki's scepter contained. He is holding Quicksilver (Aaron Taylor-Johnson) and Scarlet Witch (Elizabeth Olsen) as prisoners, giving us our first look at these two anticipated additions to the Marvel cinematic universe. Here, we see Quicksilver using his super fast speed to bounce from one side of his cell to the other, while Scarlet uses her mental powers to build blocks. Von Strucker proclaims, "The Age of Miracles is upon us!" And this is how mutants will be set up in the Disney owned movies.
There is a second post-credit sequence, which finds The Winter Soldier learning about his true identity. That sequence was directed by Captain America: The Winter Soldier's own Joe Russo and Anthony Russo.