I've only recently found a voice for Lucinda that I'm satisfied with, though there are plenty of songs that remind me of her.
Florence Welch of Florence and the Machine fame, is sort of my real life Lucinda. She has those dark eyes, that elegant yet wild hair, and that slightly etherial manner I'd want in a real life Lucinda, as well as the perfect voice.
The song Cosmic Love is especially appropriate for Lucinda: http://www.youtube.com/watch?v=tfBY96qxVRQ Just look at the Album Cover. That's pretty much how I imagine Lucinda looking.
I have yet to find a famous voice that could fit Knull. I don't have enough songs to listen to when I draw Knull. It's hard to find that fatalistic, fearful, yet persevering mood that personifies Knull. The closest I've been able to find is Falling by Lemon Demon: http://www.youtube.com/watch?v=CKUngEUGfLUUploaded by admin at 03:14 on 06 October