That's a hard choice... So I'll put the ones I had never gotten bored of hearing...
Japanese:
Ayu: mmm.................... (sooo many
) "Is This Love?" "To be"
"end of the world" "evolution" "Hanabi II" "Memorial Address"
Hikki: "Deep River" (despues "dareka no negai ga kanau koro" and "Hikari")
Namie: "Never End"
Koda: "Yume No uta"
Yuna Ito: "Precious"
Drama's themes: "only human" of K
English:
Mariah Carey: "Butterfly" "My All"
Kelly Clarkson: "Sober"
Christina Aguilera: "Fighter"
Whitney Houston: "I have nothing"
and a lot more songs...