I don't actually like many women vocalists, but these are some the the very few I rate:
Ella Fitzgerald
Judie Tzuke
Karen Carpenter
Natasha Atlas
Sandy Denny
Lulu

And of the blokes, these few immediately spring to mind though I bet I've forgotten some obvious ones:
Paul Rodgers
Marvin Gaye
Michael Jackson (when he was pre-pubescent)
Ian Gillan
Tom Jones
Roger Daltrey
Seal
Steve Perry

I'm also unfeasibly fond of:
Nick Drake
John Martyn
Neil Young
Though none of them what you'd call 'great' voices.