Klaus Meine. He has always had an incredibly powerful voice. He may have lost a lot of that, but is still pretty incredible from what I have seen online.
I would also add Michael Sweet. He has taken such good care of his voice, and I daresay he sounds better now than he ever did. He neither looks nor sounds 52.
On the opposite end of the spectrum we have Ozzy, Axl and DLR Geoff Tate.
Fixed.
I agree on Klaus Meine so much. To me, the difference between his voice on their most famous studio performances is minor since they always tried to make him sound a bit soft either way, so he still sounds impressively powerful for a man that's almost 70 years old (!). There's a huge difference between a 70's live performance of Sails of Charon and his current sound, of course, but that's obviously to be expected (there's that one amazing performance of this song by the way, blows my mind almost as much as '92 JLB every single time).
But man, his vocal range. So incredibly consistent. Rarely screws anything up, always in tone. That man is incredible.
I have to say that JLB impresses me far more than, say, Bruce Dickinson or Rob Halford. They're all amazing for keeping their tone and sound so late in their career, but James' ability to nail most of the notes, from the highest to the lowest, and hold his breath for as long as he needs every time, impresses me far more than, say, the way Dickinson has to force himself to alter the rhythms so often (with all due respect, and there's PLENTY). I just really think James goes above and beyond most other vocalists to maintain his health and voice over the past few years, and it shows so beautifully on stage...except for some off-nights here and there.