Obviously Ayu but, that's why I'm in this forum in the first place xD SO:
Shiina Ringo: I first heard Karuki Zamen Kuri no Hana and gosh it was very different, I wasn't so into it, and I'm not so so fond of the album now, maybe just a tad too dark for me, then I heard Shouso Strip and that did it :3 I love her now.
Koda Kumi: I didn't get crazy over her through Final Fantasy xD In fact I'm not very crazy over her at all, but I heard Black Cherry and I gained some interest in her, then I heard disc 2 from her 1st Best CD I believe, Cutie Honey and a few other songs just got to me, loved it xD
Chihiro Onitsuka: Another great one, I first heard her and I was like, BLEH but after a while, she got to me too, her voice is precious that's all I gotta say ^^
Rurutia: She's got one of the most soothing voices ever, and her music makes the effect even greater
I honestly love Ruru as well >w< (Hehe, I've been wanting to call her that for a while) Oh, and I didn't like some of her stuff before, it was as soon as she was recommended to me by another thay I got into her.