I've never really looked into the names of vocalists... woh, I feel dumb right now.
Anyway... I'm surprised no one said:
James LaBrie (DT)
Tony Kakko (Sonata Arctica)
Mats Leven (YJM)
Michael Vescera (YJM)
Stu Block (Into Eternity)
Brad Nowel (Sublime)
Whitney Houston - don't laugh, it's true!
Warrel Dane (Nevermore)
WORST:
Ozzy
ZP Theart (Dragonforce) <--- his vibrato is this annoying purr...
Tom Delonge (Blink 182)
Joseph Trohman (Fallout Boy)
Whoever the singer for Coheed and Cambria is. (what Mastodon said!)