BUMP OF CHICKEN, KAT-TUN, Arashi, NewS, Otsuka Ai, NYC, A.B.C-Z, AKB48,and Kis-my-ft2 are ones I often listen too! IF it's any help, you can listen to popular japanese music, and find new artists and other songs here:

<a href="http://www.jpopasia.com/charts/">http://www.jpopasia.com/charts/</a>;

CHAGE&ASKA(^^* 

L'arc~en~ciel <- I definitely agree with this one. There lyrics are mostly japanese with some english. Favorite song by them: Coming Closer

Gackt <-- He is really good and also known for his work for some video game music (FF: Dirge of Cerebrus is one). Favorite song: kimi ga matteiru kara

Susumu Hirasawa <-- He has done work for anime movies and running anime shows. Examples: Berserk and Paprika. I really like the song Girl in the Byakkoya by him.

Bump of Chicken <-- I've only listened to a couple of there songs. They did the opening for a game called Tales of the Abyss.

Others that I have listened to one or two songs from:

Do as Inifinity by Fukai Mori

Still Doll by Kanon Wakeshima

A Rising Tide by Okino and Shuntaro

Complication b<em>y </em>Rookiez is Punk'd

I second that ... :)
Actually , i started to listen to Arashi because of the opening songs of Hana Yori Dango .. :D

ARASHI for sure !! try it ^_- ~~