Muireann Nic Amhlaoibh has the best voice, I even bought one of her CD's although I don't understand a word, like Kathleen MacInnes, the sound of the voice is enough.

Some more - Gillian Bowman, and nobody can beat Sylvia Barnes for emotional feel in a song. The aforementioned Robyn Stapleton is wonderful too, and Emily Smith is one of very few people I have three CD's of.