In an article posted on MTV's Splash Page, screenwriters Chris Markus and Stephen McFeely discussed their ideas for the sequel to this summer's Captain America: The First Avenger, which has currently grossed almost $316 million worldwide. Although the character of Steve Rogers was brought into the present day at the end of the first film so that he could be included in next summer's The Avengers, there's a very easy way to tell more Captain America adventures set during World War II.
According to McFeely, “The span of [Captain America: The First Avenger] is about two or three years, and there’s a few times in the film where you jump four months ahead, you jump six months ahead. So we did that with the intention of saying, ‘Okay, there are certainly unseen adventures that Captain America went on in that period that if we want to, we can go back and explore later.’”
With actor Chris Evans reportedly already signed for two more Captain America films and two more Avengers films, it shouldn't be too hard to envision the next Captain America movie arriving in 2013, presumably followed by an Avengers sequel in 2014 or so. And with the Avengers set in present day, keeping the setting for the Captain America films in World War II might be a way to distinguish them more from the Avengers movies.
If they do, however, decide to feature the next Captain America film in the present day, Markus has enthusiastic thoughts about using Peggy Carter's niece Sharon Carter and Cap's occasional partner The Falcon as modern-day supporting characters. Markus remarked, "I want both of them! Sharon is meaty, almost to a point where you get a little uncomfortable because her relation to Peggy has shifted over the years, as time has passed...You have to walk a fine line there because it does seem like you’re dating your girlfriend’s daughter." As for The Falcon, Markus shrugged off a 1970s setting for the two heroes, but said, "It would be awesome to go straight up like Shaft with Cap and The Falcon."
No announcement of a scheduled release date has been made concerning the sequel, although the project was confirmed by Kevin Feige, President of Marvel Studios, back in May.