If I recall correctly she was pretty decent as the Wicked Witch in Wizard of Oz at Madison Square Garden...what...11 years ago? Though she didn't have a song and at the end when the whole cast sang "Somewhere Over the Rainbow" I'm pretty sure she was just moving her lips.
Tracy Ullman is a great suggestion. She was great in Once Upon a Mattress with Matthew Morrison and Carol Burnett.
And yes...Bonnie Hunt had a sitcom that didn't last long and, if I recall correctly, she was a talk show host. I only remember seeing one episode.
As for Kathy Najimy - I think more people know her than we realize. Hocus Pocus, Sister Act, WALL-E, the upcoming Tinkerbell, and she's the principal on "The Suite Life of Zack and Cody" which is a very popular show among the tween set. A demographic the theatre seems to be reaching out for more and more. She's one of those actresses who seems to always be "around". People may not know her name but they know her. And I seem to remember her singing in "Cinderelmo" when she played the Stepmother.
"All our dreams can come true -- if we have the courage to pursue them." -- Walt Disney
We must have different Gods. My God said "do to others what you would have them do to you". Your God seems to have said "My Way or the Highway".