Evaluating singers (as opposed to other instrumentalists) is an interesting excercise as they are the instrument-maker as well as the player. I may not have the equipment/ears to discriminate between "almost perfect" and "pretty good" recordings, so please excuse any proposed inclusions which don't sound quite so splendid with a real "audiophile" set up.
I'd suggest to add:
* Frank Sinatra / The Coffee Song / Ring-a-Ding-Ding! / (the latest re-mastering, which I think was 2010 or 2015)
For my money, Johnny Mandel's arrangements are even more perfect for Sinatra than all of the other first class arrangers with whom he worked. The song's range is perhaps a semitone too deep for his voice to remain perfect throughout, but if someone were to write a book on the best use of vibrato, I can't imagine it being anything other than an instruction to listen to this cut on repeat a bahzillion times.
* Kurt Moll/ Das Thal / Die Orchesterlieder (Strauss) / 199x?
As an "instrument-maker", I think Moll was the greatest bass I've heard. I find he scooped a bit more than I'd like, but the recording against an orchestra I think gives an impression of the sheer solidity of his voice in a way that his lovely recordings of Schubert's lieder, for instance, don't.
* Mel Tormé / It's de-lovely / at the Red Hill / 1962 (my recording may be a re-mastered one but I only patchily recorded some of my metadata when I ripped my compact discs a decade a go).
With all the respect due to one of the greats, I am not convinced that Tormé had the best taste/judgement when it came to his own recordings. Personally I don't think his timbre suited a big backing band, and I can't really enjoy a full 40 minutes of uninterrupted crooning, but with a smaller backing band and a more diverse mixture of sentiments and tempi, it's hard to go past "the velvet fog". I think this track really captures his tremendous technique and timing, and shows how beautifully his tone actually went with more up-beat numbers. His mic work perhaps wasn't quite studio-still, but that's live recording for you.
* Bobby McFerrin / Opportunity / Spontaneous Inventions / 1986
I don't think McFerrin is as great an "instrument maker" as some of the other suggested inclusions here, but his technique and technical innovations put him in a league of his own.
* André Minvielle / Flambée Montalbanaise / Paris Musette / 1990
Minvielle has, I think, the perfect musette voice: it sounds like a galoise. Unfortunately for my reactionary tastes, most of his recorded music is pretty avant garde.
* Darryl Hall / Do What You Want, Be What You Are / Bigger than both of us / 1976
I happen to love a lot of Hall & Oates more maligned 80s work, but I also love disco, so possibly I'm not the most tasteful person in the world. This song, however, demonstrates the best of their work, and Hall's pipes. The gimmicky L/R antiphonal effects on the echo at around 90 seconds also helps you identify if both of your speakers are working as a bonus.
* Kurt Elling / Steppin' Out / The Gate / 2011
There are many more tracks which showcase Elling's bop technique and sensibilities (I've had the pleasure of seeing him live a few times now, and I would not be surprised if he is actually a time-traveller from 1958), and I'm not a huge Joe Jackson fan, but I think this really brings out the tonal qualities of his voice, especially the mixture of resonant smoothness and then the slight husky prickle in his higher register, almost like 5 o'clock shadow.
* Barry White / I Found Love / The Message is Love / 1979
Everyone needs some sweaty disco/soul jams in their library, and from the sine qua non cheesy parlando introduction to the over-produced mille feuille of disco hooks, The Man's unqiue voice just fills this track.
