Madonna
Mariah Carey
Whitney Houston
Shania Twain
Celine Dion
Edit: Oh, Grammy's. Then all of these are screwed lol. Nonetheless these are the first names that popped up in my head. They each contributed to changes/transitions in pop music and saw great commercial success.
Today's artists are so much more than musicians though. Mariah, for instance, made a huge bulk of her money off her music alone. Today you have the girls (yes, including present-day Mariah) doing perfumes, clothing lines, nail lines, etc. Different times. And with social media constantly evolving, promotion is so much easier and easily accessible. So, in naming the top five females, you'd have to take that development and the benefits it brings into consideration.
I think Britney might deserve a mention as well, seeing how big of an phenomenon she was. Beyoncé, one day.
