I'm sure you're all tired of hearing it by now XD
Originally, Marvel had planned on doing a Black Widow solo movie first- yup, before Iron Man. They ended up canceling those plans because Aeon Flux, Elektra, and Ultraviolet were all female-led action movies and they... tanked. And the studio attributed it to the fact that women were the protagonists (not the confusing plots or less-than-thrilling storylines). And to this day, I'm one very cranky fan, lamenting the movie that never was.