I don't care for LuPone, but as I've stated way too many times in the past few days, her "Being Alive" is stunning. (See? Sondheim can write big belting songs as well as the next guy.)
I don't know if Bernadette Peters can be considered a traditional belter, but I love her sound in
Sunday in the Park With George, as well as the vulnerability she brings to "Not a Day Goes By."
Of course, Ethel Merman is
the belter. I have to give her kudos for sheer power, if not for modulation.

Jennifer Holliday is a pretty obvious choice as well.
I'm going to stay away from Idina Menzel. I think I've made my feelings on her and her "belting" pretty clear. If we must take someone from
Rent, take a "Seasons of Love" soloist.
D. Jamin-Bartlett sounds great in "The Miller's Son." Tonya Pinkins definitely has a big-time voice to have done the role of Caroline for as long as she did. Roz Ryan shows a tremendous belt in "When You're Good to Mama." Then, of course, there's Ann Harada in "The More You Ruv Someone." :P