I think its important to notice that the thread asks which puppeteers have BEAUFITUFL singing voices. Now there are some singers who can be very impressive, but would you call their voices beautiful? There are also singers (and this is particularly true amongst the muppeteers) who may not be particularly versatile or necessarily great singers, but their singing is still beautiful.
Anyway I think my answer to the question would have to be: Jim Henson, Steve Whitmire, Jerry Nelson, and yes, Louise Gold.
That said some of the others have had their moments too (such as Dave Goelz on ocassion - listen to his recording of I'm Happy To Be Me for example). While Richard Hunt was generally a pretty good all round singer.
Jim Henson and Steve Whitmire have a way of doing a song very simply and beautifully, listen to: It's Not Easy Bein' Green, Rainbow Connection, or, Have Yourself A Merry Little Christmas - there is a really beautiful quality there.
Jerry Nelson and Louise Gold are both very versatile singers, with quite a range, that includes beautiful as well as amazing!
In fact Louise Gold is a rather interesting example of a wide ranging singer. On the one hand she is very loud and brassy, a real Merman-Style belter As Aline Waites once said "Louise Gold it has to be said achieves the impossible, she makes Ethel Merman look subtle". More recently of course on the West End stage she tends to play rather unplesant characters with a growling voice.
Some else on this thread mentioned her alto, - and it might be mentioned that in the film Topsy Turvy she did of course play the role of the 'Principal Contralto'.
Yet besides that loud brass, as well as some of her other more bizarre singing qualities (much in evidence on the film Billy The Kid And The Green Baize Vampire, as well as numerous puppet programmes) she can also be aremarkably sweet, subtle and sophisticated singer. She's proven that many a time, handling sweet simple ballads by the likes of: Kurt Weill, Rogers & Hart, Stephen Sondheim, Jason Carr, and even (in her cabaret act) Paul William & Kenny Ascher - yes the Rainbow Connection. However, there is one occasion where even I was surprised at just how beautiful a singer she really is, and that's on The Secret Life Of Toys, she was performing Dafodil in SLoT and sang a song (music by Peek-a-boo, lyrics by Jerry Nelson) 'Light Will Make It Bright'. It is one of the most beautiful pieces of singing I've ever heard, and for a long time I honestly wondered which puppeteer it was; until by chance discovering it was in fact one of Louise's performances!
Best Wishes
Emma