According to ComicBook.com on March 15, Easter eggs that could be considered movie spoilers by some fans had been revealed in "Captain America: The Winter Soldier". Word had made its way around from numerous press screenings and through celebrity interviews. References to characters, architectural constructs, and other tidbits of interesting information in regards to a future film had slipped their way into the movie.
A glimpse of Stark Tower is made apparent in the film as noted in an interview with Kevin Feige.
“You get a quick glimpse, I don’t know if you noticed, of the new Stark Tower – which is not the Stark Tower it’s the new Avengers Tower in Captain America: The Winter Soldier. We show it in there. It goes by *snaps* real fast during that targeting sequence. But it’s there".
Also, the film entails a "shout out" to the Doctor Strange character. According to Marvel Studios, a film dedicated to this character and is currently one of the films under development for phase three. That being said, "Captain America: The Winter Soldier" is thought to be first film to make an official reference to Doctor Strange.
More importantly, is that the set up for "The Avengers: Age of Ultron" is revealed in one of two of the post credits teases. Both Scarlet Witch and Quicksilver make their appearances at the end of the film. The end-of-credits clip was also directed by Joss Whedon.
Finally, a reference to Iron Man is made in the film. A portion of the film shows a dialogue between Nick Fury and Alexander Pierce, played by Robert Redford, refers to a personal favor that Fury requests. In response, Pierce wanted a favor done in return.
“Fine, but you’ve got to get Iron Man to stop by my niece’s birthday party. And not just a flyby, he’s got to mingle".
"Captain America: The Winter Soldier" opens in theaters April 4.