kawada mami, kotoko, kuribayashi minami, YUI, have loads of japanese songs in my mp3 sense by kawada mami is good to hear
those are nice i like the current line up in I've which is Kawada Mami,kotoko,Kaori Utatsuki,MELL and Eiko Shimamiya
Back - ON, LM.C, Nana Mizuki, Kazuki Kato, Keita Tachibana, W - inds, and a few other songs from anime openings and endings
I like the ending song of Darker than Black preformed by Rie Fu with the song Tsukiakari http://www.megaupload.com/?d=RDVW6K26
most stuff by Maiko Fujita and startoftheday but they're hard to find i think >_<. Oh and KELUN is awesome too (^_^)