My favorite poster will always be Les Mis. I thought it was just gorgeous.
Sendak's Into the Woods poster was not only gorgeous, but the fact that he was selected to design it was inspired brilliance. The last time I saw it for sale was for $350.
The poster for the revival of An Inspector Calls (with just the telephone) was beautiful. It's impossible to find now.
I also loved the logo for Carrie. I've been trying to get the poster for years.
The original design for The Scarlet Pimpernel (gloved hand covering face) is artistically stunning.
I also thought the Haring design for Falsettos was a brilliant choice.
Probably the most effective use of logo in musical theatre history has been the Phantom mask. All over the world, people know what it is. Second would be the Cats eyes.
"What can you expect from a bunch of seitan worshippers?" - Reginald Tresilian