I'm really into the heavier side of J-rock, but I've got a soft spot for Moi Dix Mois, Malice Mizer and An Cafe.
If you want heavy, check out Black:List, Yaminade, Reivier, Unsraw, CoRe the Child, -OZ- and Nega, to name a few. Unfortunately, most of these bands have disbanded, Nega being the one that is disbanding this April I believe.
Check out Shattered-Tranquility: http://shattered-tranquility.net/
They've got up to date news on tons of Visual Kei bands, events, lives, all kinds of shit, and the mods post something new almost every day. I've found out about quite a few bands from there, and it's always interesting to hear about new upcoming J-rock bands.