Myles Kennedy probably has the most impressive range I've heard. His voice is almost always perfectly in tune, even when live, over a ridiculous range. Some of his covers of Guns and Roses songs are just unbelievable. I always have a soft spot for the old crooners like Sinatra and Dean Martin though, even though their singing isn't technically all that it is just a joy to listen to, which is kind of the point imo. Female, I'd probably Nina Simone, just love the way her voice sounds.