my favorites are:
Robert Plant
Ian Gillan
Freddy Mercury
Bon Scott
Brian Johnson
Glenn Hughes
David Coverdale

Almost all of them have a great range...
especialy gillan, which in my opinion was the greatest vocalist of his era...
Just listen to made in japan - child in time, and strange kind of woman - He's doing just great vocals there...
Freddy - not much to say... great range, tough he didnt sound to good on concerts...
all the others are just great vocalists... nothing much else to say...