It's no secret that Marvel has thought about making a standalone Black Widow movie with Scarlett Johansson. I'm sure it will happen eventually, but according to Marvel Studios President Kevin Feige, even though they have been discussing ideas it won't happen anytime soon. He was asked about it at the press conference for Captain America: The Winter Soldier, and this is what he said:
"I think it could be great. We've got various outlines and ideas of where to take that. As Scarlett's already said, there's a big element that explores her backstory in an upcoming Marvel feature. So the question really is, 'When do we want to take her out of the ensemble to go and do her own thing?' As you saw in [Captain America: The Winter Soldier], as you'll see in Avengers: Age of Ultron, she's really the key to so much of the broader world."
Apparently, the end of Captain America 2 perfectly sets her up to do her own thing, but from what we know that will carry into Avengers: Age of Ultron instead of Black Widow 1. I'm happy that they are building this character up in the Marvel cinematic universe as she's one of my favorites. I'm sure when she gets her solo movie it will be awesome.