Another vote for Steve Perry. A few other names that pop into my head:
Chino Moreno (Deftones)
Corey Taylor (Slipknot, Stone Sour) He's, I think, a little underrated as a vocalist, but he has tremendous range
Layne Staley (Alice in Chains, Mad Season)
Tatiana Shmayluk (Jinjer) Not going to be...