Wow. You only have three on here that are worthy of the term "great." Rob Halford, Freddie Mercury, and David Lee Roth, I agree...are legends. But the others you listed here, are jokes...and entirely overrated.
Hansi Kursch from Blind Guardian, Tony Kakko from Sonata Arctica, and Eric Adams from Manowar belong here too. And I agree with John Doe that Plant is a vastly overrated singer.
As a suggestion: Michael Kiske ex-Helloween.