Hi,

here's my favorite japanese Bands:
Gackt / Moi dix Mois / Malice Mizer
Hyde / Tetsu 69 / L'arc~en~ciel
Dir en grey
Kirito / Pierrot
Hide / Yoshiki / X-Japan
Raphael / Rice

X-Japan, Malice Mizer and Raphael do not exist anymore *cry*, but since X was a very popular band, same as Malice Mizer, you can still find lots of their music. So sad Hide of X had died years ago, but you still can find songs he had performed with a band called "Spread Beaver". Gackt, who was Malice's Vocalist, now has his own Band, GacktJOB, and Moi dix mois is Mana's Band, who was on the guitar for Malice. Raphael is really hard to be found, they disbanded when their guitarist died, but the remaining Members have established Rice.

Some more bands I have heard of:
Mucc
Glay
Gazette
Kagrra
Ayumi Hamasaki
Onitsuka Chihiro

Some of these bands are what is called "Visual Kei" bands, what means they might or will appear in a very glamorous, excentric, unusual style - just find out by yourself...

Hope this was a little help for you *smile* - enjoy the music!!!