Scarlett Johansson has said she's "hoping" for her own Black Widow spin-off from Iron Man 2, and Marvel's President of Production Kevin Feige agrees. Feige told ComicBookResources that Johansson is not only "signed on" to appear in The Avengers, but also her own Black Widow movie "should we be lucky enough to have an audience that wants to see" it.
Marvel likely won't have to worry about finding an audience to appreciate Johansson in a skin-tight, black leather outfit (there might be one, Marvel, fingers crossed!), but whether Johansson can make it through another movie unscathed. While Johansson enjoyed playing a "badass" character, she told IrelandOnline that the physicality of the role came at a price:
I had such a great stunt team who were unbelievably supportive. I have to say though, I'll probably never be able to turn my neck to the left again.
Luckily for her, in a comic book movie not being able to turn one's head isn't necessarily detrimental. It worked great for Christian Bale in The Dark Knight.