Well, if we talk about female singers...
Rihanna, Madonna, Britney Spears, Cher, Bjork, Celine Dion, Alanis Morissette, Lauryn Hill, Alicia Keys, Nelly Furtado... (i don't love or even like them equally tho)
maybe some others, if I remember...
I would estimate Whitney, Mariah, P!nk and Christina's voices, but something about them doesn't seem so... out of line. Their voices are specific for me, yet I think their manner could (theoretically) be reproduced more likely than ones whom I put in first line. I would also estimate Shakira, Anastacia and Beyonce, but I can remember at least one another songstress who sings in a slightly similar manner.
Speaking about male performers, it's harder for me to remember at the moment
