I figured since we had the guitarist thread I'd get this one going too. Roger Waters, James Hetfield, Jim Morrison, Freddie Murcury. Not necessarily in that order, and definitely not an exclusive list, just some off the top of the head.
Let it be known that 2nd Place is a distant second. No one in Rock History has has the vocal range and showmanship of Mercurity before or since. Elvis has his place in Rock History, but not for his vocals. I know plenty of people personally with better vocal skills than Elvis.
If Ann Wilson is not the top female rock voice of all time, she's certainly in the top 3. Pat Benatar is very similar in her range and delivery.
