Broadway Ladies (current): Judy Kuhn (She has a pure, beautiful, clear voice that is incredibly expressive-I love how she can sing beautifully and convey so much emotion.) Laura Benanti (I'm kind of surprised she hasn't gotten more attention. She's got a gorgeous voice.) Rebecca Luker (I loved her in The Secret Garden and Showboat and thought there was nothing quite like her voice when I heard it.)
Other Ladies (Some Broadway of yesteryear and some opera):
Joyce DiDonato (She's a lyric mezzo with a lovely bel canto repertoire. She's also an incredible performer overall-she has acting chops that many opera singers don't. But, her voice is divine as well-she's got a rather impressive range.) Linda Eder (I echo the poster who said her-I saw her in concert not too long ago-her bridge in "I, Don Quixote" is pretty amazing-she's maintained that upper register incredibly well.) Julie Andrews (In her heyday, she easily had one of the most beautiful voices ever. I'm sad I never saw her on stage, but luckily she had a wonderful film career as well.) Laurie Beechman (Sadly, we lost her much too soon, but what a glorious voice!)
Men (Since there are fewer of them, I'll just put them together):
Paolo Szot (I spent a few enchanted evenings at South Pacific-he also got me going to his operas. He's got a lovely voice and I appreciate his performance style.) Jason Danieley (Just try not to cry during "I Miss the Music". His voice is simply gorgeous.) Michael Cerveris (I think his range is worthy of mention-he sings a variety of material and does it WELL consistently. Well, not just well, but beautifully.) Joshua Henry (He is amazing...I don't know of anyone who sounds like him. It's an exciting voice, IMO.) Jose Llana (I wish he was the King in The King and I, personally. I adore his voice and presence. I do wish he would come back to Broadway soon.)