KAT-TUN

my first j-pop suggestion would have to be KAT-TUN though recently one of their members Akanishi jin has left the band in order to go solo in the U.S  they still continue to be a band and create music
check them out if you have time they have a variety of songs though my favorite would have to be SIGNAL.
The name of the band KAT-TUN stands for first letter of the members names since the A (Akanishi) left the band, the (KA) in KAmenashi now stands for the KA in KAT-TUN
they also have a tv show called Cartoon KAT-TUN  though the show has already ended it was a great way for fans to get to know the members of KAT-TUN,

the current members include
Kazuya KAmenashi
Junnosuke Taguchi

Koki Tanaka
Tatsuya Ueda
Yuichi Nakamaru