Jeez, Lennon and McCartney. Just listen to Hey Jude.
I also love Okkervil River's Will Sheff. He's such a technically poor singer, but he sings so passionately. When he screams, his voice trembles in a way that makes each word resonate through your body and dwell in your head until you're ready to scream right back at him, with all the same power and motivation. He really makes you feel it.
Edit: I guess it really depends on what I'm listening to.
In terms of soul and blues, I love Otis Redding. In pop, can you tell me Michael Jackson isn't amazing? Elton John is a great singer, too.