Shunsuke Kiyokiba. He was from EXILE but now he has a solo career.
He has great songs like Sayonara Itoshii Hito Yo..., believe and Ningen Jarouga!
If you like ballads just download his albums. You will like it!
Wiki
Akeboshi. He's kind of traditional but he has good songs, good melodies.
He is known for his song
WIND (this song was used in NARUTO) but he has more great songs like Akikaze no Uta, Deep End, Faerie Punks, Kamisama no Shitauchi, The Audience, Yellow Moon and Morning high.
Hata Motohiro. Download his album
Contrast some songs are really great.
K. I dont know him so much. But he has a great single named
Only Human. You need to listen for sure.
Wiki
Ryohei. I just have his album
ReListen. This album is really great. It has many acoustic covers and some good ballads. I love the song (and single)
You Said....
I know some guys who sings ballads but I dont have their stuff.
Tachibana Keita (he is from the boy band W-INDS)
Suga Shikao