I don't like David Lee Roth, but I guess he does deserve to be in the discussion. And Freddy Mercury did at least have a couple of years in the 80's, though his best work was in the 70's... so he should still qualify, and he was one of the greats-- without doubt.
For rock, I'd put Axl Rose & James Hetfield... and probably Bon Jovi over Vince Neil and other hair metal guys.
Robert Smith & Morrissey were probably the best front men of that genre. Honorable mention might go to Ian McCulloch of Echo & The Bunnymen-- he had potential, but I'd say he was still 2nd tier... I sort of think him the British alternative music/new wave doppleganger of Rick Ocasek, who is also 2nd tier imo.
I don't think anyone mentioned Sting from his The Police days. I'd rate him above Stipe, but that's a matter of personal preference.
eta: Bono should be in the list of the best, too.
This post was edited on 1/21 at 12:08 pm