Ooooohhh yeah!

My amarok artist listing, bold on all japanese ones:
Various:
*Final Fantasy VII OST
*Tribute to Avril Lavigne-Master's Collection-
Yuu
Younha (korean, but many songs in japanese)
Gazette
Nightmare
Chirinuruwowaka
Porno Graffitti
AKB48 (only one single though)
Avril Lavigne
Azian-Z (nothing I actually listen to though)
Dir en Grey
Evanescence
GO!GO!7188
Gorillaz
kaggra,
Linkin Park
little by little
Marilyn Manson
Rammstein
S.H.E (Taiwanese singing chinese)
Tommy february6
Tommy heavenly6
W
zentrix
Nakashima Mika (never listen to her though)
Kusumi Koharu (BALALAIKA! <3)
Alice Nine
Koda Kumi
Morning Musume (not listening to)
Kimura Kaela
Shiina Ringo
Chou Hikou Shounen
Miyavi
Kana

EDIT:
btw, I'm also a proud keeper of the following Japanese retail albums:
Kimura Kaela - KAELA
Kimura Kaela - Scratch
Kimura Kaela - Circle
GO!GO!7188 - Parade