It is good to find this thread, though I'm WAY out of tune with regards to most of the singers mentioned. (I gave up listening to radio years ago, because the commercials gave me headaches.)
It was nice to see such people as Joan Baez and Simon & Garfunkel mentioned though. They've done some of my favorite songs.
I also found the scale warmup and voice soothing concoction mentioned in one post to be right in line with what I had been thinking about doing. (Well, I hadn't thought about the voice soothers, but as a fan of lemon and cherry drops, any strain on the voice would have me reaching for those or the equivalent.)
Another possible source of music featuring female singers would be folk music from Peter, Paul and Mary. Very singable and you can usually find the lyrics in lots of places.
If you do an octave shift like one person mentioned, groups like the Kingston Trio open up dozens of songs to your singing pleasure.
If you are into science fiction and fantasy, or Ren Faires, you might look up Heather Alexander. A great vocal range and lots of songs in a variety of styles.
She retired not long ago and has become a FtM singer calling himself the Heir.