I've grown quite a liking to some chick singers recently. Namely Sarah Mclachlan, tori amos and pj harvey.
i know it may be a little sad, but i quite like dido and jewel as well
Also the chick from evanescence or whatever they're called? she makes the band much better than they are, IMO. That's just stuff i hear on the radio though, i don't actually have it.
most of the time i find it good music to study to, because it's quite relaxing, so i just put in on between some sigur ros and aphex twin selected ambient works.
anyway, who are some other good chick singers! they seem to be quite underated when they're just as good as the guys singers going around.