I think that Ahrens & Flaherty write some of the best opening numbers of all time...so just add all of theirs...
I am a huge fan of Opening numbers too...I don't generally include Overtures, but opening instrumental numbers are often as integral to the show as any other more traditional Opening Number.
Some fall in between being an Overture and an Opening Number...like the Prologue in City of Angels, or the similar piece in "A Little Night Music", or "Runyonland" from Guys and Dolls.
But some of my favorite opening numbers are:
"Twenty Million People" - My Favorite Year
"We Dance" - Once On This Island
"Prologue" - West Side Story
"Carousel Waltz" - Carousel
"Ragtime" - Ragtime
"Company" - Company
"Do You Wanna Go to Heaven?" - Big River
"Tradition" - Fiddler on the Roof
"All that Jazz" - Chicago
"Wilkommen" - Cabaret
"Ballad of Sweeney Todd" - Sweeney Todd
"I Hope I Get It" - Chorus Line
"Comedy Tonight" - Forum
"Magic to Do" - Pippin
"In the Heights" - In the Heights
And so on, and so on....
Baritone in search of a role in a new musical...