Greatest voice ever?

Gregory Peck!

I have to laugh because I have just watched an episode of Barney Miller. It's one of Steve Landesburg's first appearances on that show. He was another character before he took the role of Arthur Dietrich...... however, when he first appeared as Dietrich, he was asked to use a manly voice. When he did, he sounded just like Gregory Peck. It was uncanny and hilarious!
Gregory Peck had a very distinctive voice and a way of talking. There is no mistaking him.....
Unless you are Arthur Dietrich..... LOL!

Frank Sinatra

I would have chosen James Earl Jones for best male voice, but he's already been mentioned, so...

Ted Levine
Demi Moore
Barry White


If we're (oddly on this movie chat forum) including singing voices:

Lou Rawls
Sarah Vaughn

I'm not claiming the two above have recorded my favorite songs--not at all. But for sheer vocal greatness, they are supreme. I find Mark Knopfler to be the most emotionally effective singer, and Art Garfunkel/Paul McCartney to have the most limber voices. Karen Carpenter is (at least off the top of my head) probably my pick for most emotionally effective female singer. Ella Fitzgerald has the most gorgeous, limber vocals. But enough of this music talk. I'm on a movie board.

James Earl Jones for his speaking voice.

Ella Fitzgerald for her singing voice.
Honorable mention: Patsy Cline.