Boy I hate to be a newbie and bump a 1 month old thread, but this is something I actually thought of very much and with the help of my daughter even though is only 19 has some professional training and experience as a singer and dancer. I came up with my top 25 or so covering all rock and pop genres, even including Marin Gaye, Geoff Tate, M. Jackson, Gordon Lightfoot, Ian Gillan (which in his heydays was most probably the most naturally gifted rock singer and makes it at # 2 on my own list, Jesus Christ Superstar is a gem) and without a doubt with a very large margin was also my # 1, Freddie Mercury.
Yes he covered 4 octaves (and actually some more but was not advised to use that as it would have been detrimental to his voice), yes he was if not the most, in everyone I know top 3 list of performer, entertainer. But it's the way he traveled with rock in a way that as since not been seen, having fans from all walks and genres and it was ok for everyone. I had the immense pleasure of seeing him 5 times live (I was there on the blu-ray nights).
My daughter listens to everything and loves vocals and she thought that Freddie was so gifted that he made you forget just how awesome he was, and I give her credit for hitting it on the head.
Thanks for baring with me.
penta