Most unusual/mesmerizing female voice.

Try Sunny Sumter's album Sunny on Mapleshade records. The first song called Nick of Time is mesmerizing. 

I like her voice but I mistook her name (see my post above): she's obviously Kate Pierson, not Pearson*.

as I'm here, I also add some other votes:
Sinead O'Connor
Mimi Parker (Low)
Margo Timmins.

*q: is the pronunciation very different or quite the same ? my English is bad and I often mistake in these cases

Silvana Ida of Apoteosi, 1975
Annie Haslam of Renaissance II, 1972

are angels

Jane Duboc of Bacamarte, 1983
Jane Relf of Renaissance I, 1969

Rocker:
Inga Rumpf of Frumpy & Atlantic,1970

Good hit on Yma Sumak!
I’ll add:
Diamanda Galas
Nina Hagen
Anita O’Day
Gretchen Parlato
Guesch Patti
Julee Cruz

Teresa Salgueiro;
Lisa Ekdahl;
Cat Power;
Feist;
Whitney Houston;
Beth Gibbons;
Carla Bruni;
Sky Edwards;
Dani Klein;
Ana Moura;
... ... ...