Always loved Geddy Lee's voice, one of the pieces of music that still makes me laugh is when he sings
"DON'T ANNOY US FURTHER !". Great expression and capable of surprizing tenderness {'Madrigal', 'Tears', Lakeside Park'}, wildness {'as every nerve is torn apaaaaaart !'} and unbridled joy {'A passage to Bankok'}.
Ditto Mick Jagger and Bob Dylan. I'm often surprized when people say they can't sing. They can. And John Lydon in his Pistols days, not a particularly tuneful singer but he could sing. Most of the punk singers could, actually.
It's quite difficult to find a singer who genuinely cannot sing. Even Lou Reed could sing once in a while although his voice, to my ears is genuinely awful.
If you were to put a gun to my head though, the award of 'chief voice suckatiousness' would have to go to the late Tony Williams. His drum playing was revolutionary, he helped move jazz into uncharted waters. He could play straight bop, he was at home playing free jazz, he was one of the figures instrumental in the evolution of jazz rock fusion with his band Lifetime (that at one point included John McLaughlin, Jack Bruce and later, Alan Holdsworth) but he absolutely wrecked some of Lifetime's revolutionary music with his ^%£$"!!++&^ awful singing. If his singing could've sucked more, he'd have been a hoover.