I'll recommend KinKi Kids, their songs are really great! Almost all their singles and albums never fail me
And for J-rock, L'Arc~en~Ciel for sure!! I think they have more of the commercial type of rock songs. And I can't explain how much I love their music..they are just fabulous!
Hyde's solos are also fantastic!
And for male R&B, Ken Hirai is a must listen~ Recently I also started to listen to Chemistry's (R&B duo) music, and I love their 1st few singles (Pieces of a dream, Point of no return) very much
You may also try listening to some songs by Orange Range, Porno Graffitti, Janne da Arc, GLAY, Fukuyama Masaharu (i love most of his old songs like Hey!, Heart, HEAVEN, Squall etc)
I'm glad to see many recommendations here! i will try some too!