Koshi Inaba...his voice is the most versatile I've ever heard. In terms of pure singing abilty, there may be others more talented. But listen to his singing carefully and you will find his singing full of subtle nuances. He matches his voice perfectly to whatever song he's singing, filling it with such emotion that he sucks you in and puts a spell on you. I can and do listen to his voice all day. He puts so much variety, emotion, and passion into his singing that it is just magical. His voice is addicting, intoxicating, and every wonderful adjective you can think of.
An added bonus is a wonderfully sexy speaking voice, and a face and body to die for. But truthfully, I would be happy even if I didn't see him and could just listen to his voice.
Here is one of my favorite pictures of Koshi.