Most of em have been posted here, I'd like to second
Koda Kumi - TABOO, seriously my most addicting song ever after ayu's evolution and Mirrorcle World!
Also:
Shibasaki Kou - Ikutsuka No Sora
beautiful song. "sayounara, sayounara..."
A bit more rock, alternative, VERY good even if you don't usually like it:
Tommy Heavenly6
- Gothic Pink
- Lollipop Candy Bad Girl (my favorite
)
- pray (also very good!)