Not Broadway, but in the new production of Little shop of Horrors in London, about 5 ensemble members come out onto the stage as tramps etc. and its just relly fun to watch. This is about 10 mins before the show starts.
I don't know if this counts, but I love how the La Boheme on Broadway sets up the second act. During intermission you see all these huge, beautiful sets coming down from the fly space with the House Manager orchestrating it all and then she says Lights Up and the whole theatre goes dark except for hundreds of lights bulbs all around the house and theatre and the show starts. Completely magical and transporting.