I'm not sure if this band is classified as J-pop or J-rock, but how about Larc'en'Ciel? I think most of their songs are pretty good. Although I don't really like their current songs....the band's getting old. Literally.
I dont know if this is J-pop, but try Access. One of their songs is played as either the intro or ending for D. Gray-man, Doubt and Trust
I'm including in this list one-man electronic groups, as well as one man musicians because I'm sorry, but if you've released an album and have toured with a band, you're a band. At any rate: Supercar Tatsuhiko Asano Shugo Tokumaru Number Girl Yukari Fresh Qypthone Macdonald Duck Eclair Boris (only see these guys live if you want your face rocked clean off) Cubisimo Grafico Perfume Capsule YMCK Plus-Tech Squeeze Box Shonen Knife Boredoms World's End Girlfriend Mono
They aren't new but I'm surprised no one mentioned The Mad Capsule Markets, they'll rock your socks off! Fact are good too