I'm a big fan of beautiful voices, two songs that came up after reading this thread are my favorites, might post some more later:
"Theru no Uta (Theru's Song)" by Aoi Teshima
from the movie Gedo Senki (Tales from Earthsea)
2006
"Nothing Compares 2 U" by Sinéad O'Connor
from the album I Do Not Want What I Haven't Got
1990