Karen Matheson is right up there. I love Loreena McKennitt but she has a few vocal oddities which would rule her out of the perfect category. However, Loreena was more impressive in concert than Karen Matheson, who I saw a few years back - Karen Matheson disappointed by staying well within her comfort zone, and there was none of the beautiful angelic high notes you hear on Capercaillie's recordings. Loreena McKennitt takes more risks and is the better performer for my money.

Also - Arlene Auger (bel canto singer, died some years back, I think). She sang Mozart's Alleluia at Charlie and Di's wedding, and it was magic.