Can't believe no one has mentioned these two: Shiho Ochida (Superfly) and NOKKO (in the 80s to early 90s)
Shiho has I think by far the best voice in j-pop/rock right now:
Superfly performing Janis Jopelin's Piece of my Heart:
http://www.youtube.com/watch?v=dKIh7...layer_embedded
Nokko - Manatasu no Ame (1987) Very unfortunate that she damaged her voice later.
http://www.youtube.com/watch?v=M0J-w...layer_embedded