I reccomend BoA - I've started at OUTGROW and went on chronologically from there but her older works are very well liked.
ayaka - she's got a powerful voice and some of her songs really are great like CLAP & LOVE
BONNIE PINK - she has some amazing songs and check out Thinking Out Loud for some of them; other songs I like are "Mint" and "Thinking Of You"
hitomi - I've recently got into her music and my current fav by her is "GO MY WAY"
I'll think of some more soon but maybe you'll like some of these
