I knew we'd get into this shit haha, okay a bit obvious but you asked for it:
For metal, have to throw Bruce Dickinson in there, too (Iron Maiden).
Distinctive as hell... No one else sounds like Bruce, but I don't know if I'd say he's a great singer. Still, his distinct sound is certainly the biggest reason for Maiden's success. Their 1st 2 albums without him were less than stellar and the albums after he left for a bit were also average.
A young Robert Plant. End of thread.