Hmmm..I don't have too many I listen too, but..here goes:
X Japan
Gackt (his older work)
Miyavi (older work as well)
L'Arc~en~Ciel
Tetsu69
Iceman
Porno Graffiti (some is J-Rock)
Luna Sea
Asian Kung-Fu Generation
Kimeru (He does mainly pop, but I do like his rock songs)
T.M. Revolution (same could be said for Takanori. He mainly does pop, but his rock is good too)
Mad Soldiers
Nightmare
Maximum the Hormone
UVERworld
That's all I can think of at the moment
EDIT: Remembered one more