Dear Greg T:
Absolutely one of the best voices ever … BUT one of the most amazing singing performances I ever saw -- and I've seen many -- was a show by voice impressionist Rich Little, who sang "Delilah" while sounding EXACTLY like Tom Jones.
Prior to that Las Vegas show, I had no idea that Rich Little could sing, but he also did PERFECT sound-alikes with songs such as "Does Your Chewing Gum Lose Its Flavor" (a Lonnie Donegan tune), "What Kind Of Fool Am I" (with the first half of the song sung exactly like Sammy Davis Jr. and the second half like Anthony Newley), plus also singing like Elvis Presley and Dean Martin.