Celph Titled probably has the dopest rap voice ever lol...
Slaine, R.A. The Rugged Man, Evidence sound dope as fukk
Apathy, Esoteric, Paul Wall, Aesop Rock, Ill Bill, Necro, El-P all have good voices
and yes there are a few with high pitched voices (which doesn't have to be bad at all)...but is that a white thing? Lil Boosie? Chance The Rapper? Bizzy Bone? etc