In the realm of epic/symphonic metal you probably can't throw a stone without hitting an amazing female vocalist. Simone Simons from Epica, Nightwish's Floor Jansen, Sharon den Adel (Within Temptation), and Zora Cock for Blackbrariar are the first that come to mind.

For folk metal there's Eluveitie with two members and Folkstone with I think one.

Very worth mentioning is Alyssa and her harsh vocals, from Arch Enemy.

While she's not been a member in a long while, I have to mention Vibeke Stene as the vocalist from Tristania, maybe my all time favorite.

For all female bands there's Girlschool, and you could say Babymetal, even if they have more members playing with them I don't know how permanent they are.

Others that I know of but haven't really listened much by would be Jinjer and Halestorm.

That's what I can think of off the top of my head, but there's so much more.

Edit: I almost forgot but I have to add: Amy Lee from Evanescence and Cristina Scabbia from Lacuna Coil.