InoriNoUta: Dir en grey FTW
For rock, I'd recommend MUCC. Like Dir en grey, they've been around for 10 years and have a bunch of albums, singles and DVDs out. All four of them are really talented and their vocalist has a great voice. Not all of their music is really heavy, they venture into pop as well sometimes.
Songs I'd recommend: Ryuusei, Fukuro no Yurikago, Gekkou, D.O.G, Haribote no Otona, Suimin, etc, etc.
Other good bands are Kagrra, Plastic Tree, Merry, heidi.