My "top 10" changes a lot, save for the top three...currently:
1.) Rob Halford: The Metal God.
2.) Dio: FI-YAH! LOOK OUT! No further explanation needed.
3.) Bruce Dickinson: Because he's awesome, and if I didn't put him on this list, he'd challenge me to a fencing duel and kick my ass.
4.) Russell Allen: Symphony X is one amazingly talented band musically, but it's Allen's vocal capabilities that really put them over the top in my book.
5.) Matt Barlow: I was pretty damn upset when he left Iced Earth. And did I ever rejoice when he came back.
6.) Ralf Scheepers: Awesome in Gamma Ray, and even more amazing in Judas Pr-...er...Primal Fear.
7.) Robert Lowe: No, not the actor, the singer from Solitude Aeturnus and Candlemass. May not have the best range in the world, but puts so much into his delivery you'd swear the man could read the phone book and make it sound like every word was critically important.
8.) Floor Jansen: I like many female metal vocalists, but Floor is the only woman on my top 10 list. Operatic capability? Check. Classic metal style? Check. Throaty blues? Check. Emotive and energetic? Check. Four-octave range? Check. Phenomenal stage presence? Check. Amazingly cool person in real life? Damn right.
9.) Geoff Tate: Yeah, okay, so Queensryche hasn't been "metal" for a while, but their early albums were incredible, and Tate's powerful vocals were a big part of that.
10.) Warrel Dane: Tortured emotive operatics? Currently on this list because I have been on a major Nevermore kick as of late and am very much looking forward to the release of The Obsidian Conspiracy.
Four Honorable Mentions: Jorn Lande, Jon Oliva, Eric Adams, King Diamond.