Yeah, I almost forgot: Ian Anderson of Jethro Tull...still have on my mind his performing of "My God" in Tanglewood in 1970.
I haven't voted because I can't narrow this down to just one person. David Lee Roth definitely is one of the greatest frontman because the guy definitely is an entertainer. Axel Rose is also one of the greatest because, let's face it, love him or hate him, the guy's got what it takes to pack a stadium. But I also think Sammy Hagar is among the greatest as well because of what his songwriting skills add to a band. He was AMAZING with Van Halen when I saw them live way back when. The above is all my opinion, nothing more. Just so y'all know... ;-)