There are different interpretations going on in this thread (as to be expected). I tried to limit mine to rock (or what I thought was close to it) music and singing voices that were strong, distinctive, and could be belted at the top without loss of quality.
Oddly enough I didn't even consider one of my all-time favorite singers, Dave Gahan, for this list. His voice is wildly distinctive and matches PERFECTLY with DM's sound and what they were trying to do. But as a pure singing voice was it really great? Honestly no. Then there are others that are very distinctive, like an Eddie Veddar or a Mick Jagger, that people love but can you really say they were truly great singing voices? I don't think you can.
Probably the best pure singing voice I've ever seen live is Anita Baker. Wow, even at her current age she can hit EVERY note, and is smooth as silk. I was blown away at how good she was and how effortlessly it seemingly came.
One of my other favorite voices is Colin Hay. He can't quite hit the highs like he used to (like many on this list including Plant and Winwood) but in his prime his ability to hit those searing highs with his distinctive voice was incredible.
Obviously this is a thread that could go on and on for most of us. I'm sure there are several people I'm omitting (as is everyone else).