I'd say the GazettE, Dir en grey, alice nine., Miyavi, LM.C, An Cafe, SuG, MUCC, The Underneath, Kiyoharu, Gackt, HYDE, L'arc en Ciel, Girugamesh, for starters.
Not Japanese, but very good: Cinema Bizarre, Jay Chou... if you might be interested.
also.. please check out this thread:
http://www.japanforum.com/forum/japa...avourites.html