Wow - tough choices...
Ray Gillen - (Badlands, Black Sabbath) - A balls out, natural, pure rock voice. Old school influences.
Geoff Tate - Incomparable career recorded and live - one of the pyrotechnicians in any style.
Brad Delp - Smooth, wide range, and I'm sure great to record and mix - pure power and emotion.
Ronnie James Dio - While not the greatest technician, the precursor grand dad to a lot of metal styles. A great blend of opera, gravel, dragons and storytelling.
Sean Verrault - (Wide Mouth Mason) - You don't know who this guy is, but apart from being a fantastic guitarist, this guy goes from blues bitching to Stevie Wonder R&B soaring effortlessly. He'd kick a** if he was in Tower of Power. Wide Mouth Mason is a great funky rock band with a blues tint. A great example of doing it all well - songwriting, singing and playing.
Those are the singers that come to mind. There are some obvious female mentions as well, but these are a few I listen to these days.
VoiceWorks Plus / Harmony G / TC Powercore / VoiceOne2.0 / VoicePrism Plus / Konnekt 24D / Harmony M /
Harmony Control - Guitar / VSM-300/200XT