Add another for Sarah McLachlan. She may not have the absolute best voice in terms of range, but it's extremely soothing to listen to her sing and that's "nice" (the criteria cited in this thread.) I personally think it's a lot better than listening to Mariah Carey see if she can make glass shatter. Allison Krauss is good too, it's just a little TOO soft for me in most cases. I also like Lisa Loeb for the cute, nerdy, girl-next door look and sound.