(as my taste in music is almost entirely vocally/lyrically driven, these are all female-sung, rather than focusing on female-played instruments)
My friends and I were all about Flyleaf when they first appeared on our radar. A girl! Who screams!
Also, in finding these videos, I find that I tend to buy vastly more music by men--female artists I like, like Tori Amos, I tend to not bother buying whole albums. I look her up on YouTube instead. This needs to be remedied!