Freddie Mercury, David Bowie and Elton John all have indelible voices.
There are not a lot of female singers in the kinds of music the I listen too. As far as voices go I really did like Pat Benatar and Joan Jett back in the day. Not my style of music, but Rihanna has a great voice. Heard her sing some old classics before and also the DC Veteran's day concert a few years back was really impressed with her range and the way she really put her heart into it.