Eh, I think driving to Berlin (which takes ~8h) in summer (aka REALLY warm) for Dir en grey's first Europe concert proves that I love J-Rock xD (+ another concert the year after that, in Cologne though)
Lemme try to think of other bands I like ...
Abington Boys School (their openings for Darker than Black and D.Gray-man are awesome <3)
Gazette
DespairsRay
Mucc
Zwei (check em out, they own =D)
AnCafe
hide (<3333333)
Hyde
L'arc en ciel
Kinya Kotani (aka all the stuff from Gravitation)
Malice Mizer
Gackt
Miyavi
X Japan
and a lot of random bands I found through anime openings xD like Nightmare, Maximum the Hormone, High and Mighty Color, etc.