there's way to many to list.
Ronnie Dio
David Coverdale
Glenn Hughes
John Bush-Anthrax/Armored Saint
John Arch-Fates Warning
Danny Vaughn
Paul Stanley
Sebastian Bach
Ray Gillan
Ron Keel
Ian Gillan
Robert Mason
Kelly Hansen
Mark/Marcie Free
Joe Lynn Turner
Jeff Scott Soto
Mats Leven
Tony Harnell
Bruce Dickinson
Geoff Tate
Mike Metijevic
Andi Deris
Michael Kiske