What vocalist sends chills up your spine?
 

Reverend Al Green- How can you mend a broken heart? I'm listening to it right now for the 4th time in a row. Feels like a spiritual experience.

Louis Armstrong - What a Wonderful World

Diana Ross- Ain't no mountain high enough

George Harrison- My Sweet Lord

These are off the top of my head. It'd be great to hear other opinions..

I like Bert Jansch, Paul Brady.

also Karan Casey of Solas has an amazing voice.

and Jacqui McShee of Pentangle.

Damien Rice-A little man crush
Sarah McLachlan-Every Single Time
Eva Cassidy-More so than even Sarah
Sometimes when my wife and I sing together, not being cocky, but I guess after you work at for so long it's nice when it flows so well,
Rafe

Last night I was re-watching A Tribute to Joni Mitchell on the VHS, lots of great performances, but I was really taken by one in particular, especially the subtle use of changes in timbre in her vocals - Diana Krall. She did this fantastic version of Joni's 'Case of You'. I know her music a bit, but I'm going to have to check her out a lot more I think.

Other notables that come to mind right away: Gillian Welch, Casandra Wilson, Betty Carter, Baba Maal

Edit: Oh, and how could I forget one of my favorite singers of all - the amazing Kathy Jordan of Dervish. Yeah!!!

the late jeff buckley
the late nick drake
damien rice
ben kweller, occasionally
chris martin of coldplay, especially on "shiver"
sinead o'connor
june tabor on "the water is wide"
elvis costello through the years
sheila nicholls
chrissie hynde
the late freddy mercury
the late nico, but not always in a good way
delores o'riordan of the cranberries

paul brady rocks. do you have or have you seen "the transatlantic sessions"?

great collaboration of bluegrass/folk/celtic players. jerry douglas joint. brady does "marriage made in hollywood." fan-freakin'-tastic.

allison kraus
steve perry
joan baez (younger version)
cher
martina mcbride
james taylor
elvis (younger version)
Frank

I'll second Allison Kraus, and also say Sarah Watkins, the girl in Nickel Creek.

Ben Kweller- How could I forget! Nice dude too!
ADAM FREAKIN DURITZ!!!!!!-My all time fav

Bono from U2... Wasn't much of a u2 fan, but after seeing their elevation tour DVD, I became totally hooked. I've never heard someone emote songs so well and with such emotion. I think their albums generally miss a lot of how talented that guy is... IMHO

Michael English - In Christ Alone, Midnight Cry, I Surrender All
Skid Row's Sebastian Bach - I Remember You, In a Darkened room
Allison Kraus
Diana Krall
Karen Carpenter

Anything from Alana Davis.

Kelly Willis. I picked her CD for a couple bucks when a music store was going out of business. Up until that point, I had never heard of her. When I heard her voice for the first time, my body went numb. Wow.

John Mayer
Norah Jones
Jamie Cullum
Damien Rice
Edwin Mccain
Jon Foreman - the lead singer from Switchfoot

Those are my favorites!

Some more
 

A lot of my favorites have been named already. I'll add Otis Redding, Sam Cooke, Van Morrison, and Aretha Franklin. Taking the question literally, Ralph Stanley's "O Death" makes a chill run up my spine.