Opera :
Maria Callas - My favorite opera singer - her voice is extremely rich, fluid, and full, even at really high notes. Her performance of "The Queen of the Night" aria from The Magic Flute is my favorite piece of opera to listen to.
Erna Sack - A singer with an absolutely astounding range - she hits the C three octaves above middle C! Even her highest notes have no trace of strain. Check out this website for some astounding singing:
https://www.dutchdivas.net/frames/highC.html.
Andrea Boccelli - He really is amazing. His voice is rich and full, and he has an astounding range - at least an F an octave and a fourth above middle C.
Broadway:
Idina Menzel - The original Maureen from RENT is an astounding belter.
Raul Esparza - another great singer.
Heather Headley - The original Aida, her voice is soulful and beautiful.
Adam Pascal - very expressive voice that sounds Broadway, but with an edge.
Everything else:
Erykah Badu - She is simply amazing. Her music is awesome and her unique voice just has an amazing fluidity that I love.
Lauren Hill - Listen to her music and watch Sister Act 2. You WILL be a fan.
The lead singer from the Cranberries - Can't think of her name but she has a really cool voice.
The lead singer from Better Than Ezra.
Daryl Palumbo from Glassjaw - I really like his vocal style.
Chino Moreno from the Deftones.
Nina Simone - amazing jazz singer
The singer for Deathcab.
Yma Sumac
ummm......
That's what I can think of right now.