Ok, so I've done guitarists, lets move on round the band to the frontmen. Now please note I'm not talking about vocalists necessarily, frontment and vocalists are two different subjects.
The reason I say they are two different subjects, is because sometimes a guy can be a horrible vocalist, but a kickass frontman (or vice versa), and in at least one case of one of the greatest frontmen of all time, he wasn't the lead singer.
The frontman, is all about the show. He's the personality. The guy people associate the band with in their heads. Some bands don't have a prominent frontman, some have nothing but; and when the frontman goes, so does the band (sometimes he takes the band with him, like Lemmy, or Alice Cooper).
A frontman may not be a great artist, or a great musician; but he's always a great showman, and usually a great star. It's not absoltely necessary to have a great frontman to be a great band, but it sure helps.
So, for this one I'm going back to hard rock only; because otherwise this field again gets way too huge... also, this time I'm going to exclude punk, because half the list would be taken up by punkers on the list simply because they were so outrageous.
So, greatest hard rock front men of all time
1. Freddie Mercury
2. Ozzy Osbourne
3. Gene Simmons
5. Robert Plant
6. Rob Halford
7. Bruce Dickinson
8. David Lee Roth
9. Alice Cooper
10. Steven Tyler
Why these choices?
Well I don't think there's any greater frontman for any type of band in all history than Freddie Mercury (I also happen to thinkl he's the greatest rock vocalist ever). The man had style, grace, showmanship, energy, crowd rapport, talnt that is only seen once in a million years... I don't think anyone else comes close.
Uhh, it's Ozzy Osborune for chrissakes. It's not like any explanation is necessary.
Gene Simmons. Well, he's Gene Simmons; like Ozzy, any explanation would be superfluous.
Lemmy? Dude, if I didn't include Lemmy there, he would, and rightly so, find me and kick my ass. Why? Because Lemmy kicks more ass than anyone except Chuck Norris. Seriously though, Lemmy has been doing this since 1965, and he still does 100+ shows a year, at full volume, and living his life exactly the way he wants to. There isn't anybody cooler, or with more cred than Lemmy.
Robert Plant simply set the mold for what a hard rock singer should be. He is the prototypical hard rock singer from 1969 onward.
Rob Halford invented heavy metal vocals... in fact basically invented Power Metal as a genre. He took gay S&M and turned it into the look of metal, which EVERY SINGLE METAL BAND ON THE EARTH then copied; which I find hilarious. He's without question the greatest metal vocalist of all time. He is, was, and will be Judas Priest (fuck Ripper Owens, and fuck Glenn Tipton and K.K. Downing for thingkint they're Priest without Halford).
Iron Maiden with Paul Dianno was getting ready to be another Diamondhead/Blackfoot/Saxon etc... and then they snagged Bruce Dickinson from Samson, and history was made. The epic, sweeping, four octave vocal metal that Dickinson made with Iron Maiden (though it was almost entirely written by Steve Harris) defined the other half of the genre. Judas preist had the rough and ready; Iron Maiden had the horror and the fantasy, and that WAS Bruce Dickinson.
David Lee Roth reinvented the rock frontman for the 80s, nothing else need be said.
Alice Cooper, was the anti-plant so to speak. He was the original heavy metal lightning rod front man. He set the mold for the ugly, dark, evil etc... bands to follow. Without Alice Cooper, we wouldnt have the Marilyn Mansons of this world. Of course the funny thing is, he's actually a remarkably intelligent, funny, pleasant guy (I've met him a couple times. He lives not too far from me, and he's very publicly active here in Arizona).
Steven Tyler, is to Plant, what Rob Halford is to Dickinson. He's the raw, gritty side of hard rock whereas Robert Plant was the melodic, and mythical side. If you look at traditional American and British hard rock, the two bands that together cover the broadest portion of it are Aerosmith and Led Zeppelin, and their front men are the archetypal frontmen.
Again, just as with guitarists, there are way too amny guys who need to be mentioned here at some point. Axl Rose, Phil Anselmo, Bon Scott, the Nuge, Marc Bolan (stretching it I know), Anthony Keidis... hell the entire universe of Punks that I left out (Johnny Rotten and Iggy Pop would definitely be in the top ten otherwise, and Billy Idol not far behind) Ronnie James Dio, Dee Snider, Ian Gillian, Hetfield and Mustaine, Layne Staley, John Bon Jovi (give the man credit for being a great frontman)...
Okay, I could jsut keep going til this list was like 200 guys long (though this one would have some women on it, like Joan Jett, Lita Ford, Nancy Wilson, Wendy O. Willams... OK I'mna stop) but it's 3am and I'm tired.
Next up, just vocalists; not specifically frontment.