Janis Joplin - her raspy, bluesy voice just exudes sex. If I could sound like anyone, I'd want Janis' singing voice.
Tori Amos - sensual and erotic and that's only while she's performing, practically making love to her Bosendorfer, she radiates beauty, and is incredibly into the music, she transcends reality
Jenny Lewis - the perfect mix for folk, indie, soul, alternative and country. Sexy, strong and brilliantly talented.
Alison Krauss - her voice is angelic, almost perfect
Sarah McLachlan - ethereal, haunting
Honorable mentions: Adele, Kasey Chambers, Dido, Jewel (on "Pieces of You")