I definitely agree with certain ones like Into The Woods, but I also have to put in a vote for West Side Story's "Prologue." Sure it's different because there's not really singing, but that's what makes it all better--most of the story and conflict is shown just through Leonard Bernstein's amazing score and Jerome Robbins' amazing choerography. I think it's still a magical moment in theatre.
"If there was a Mount Rushmore for Broadway scores, "West Side Story" would be front and center. It snaps, it crackles it pops! It surges with a roar, its energy and sheer life undiminished by the years" - NYPost reviewer Elisabeth Vincentelli