For me, the definitive best one is "Defying Gravity" (Wicked). No questions asked.
Other top ones:
- "Non-Stop" (Hamilton) - "One Day More" (Les Miz) - "Everything’s Coming Up Roses" (Gypsy) - "And I Am Telling You" (Dreamgirls) - "Where Do I Go?" and the be-in (Hair)
It's new but I have to say, "You Will be Found" from Dear Evan Hansen is so, so thrilling and moving and culmative and perfect. I could throw every adjective at it until next month, I love it so.
Ragtime. I had never imagined the ingenue being brutally murdered as part of a finale and it stunned me. Then the concluding "Till We Reach That Day" is deeply, deeply moving.
I agree with many of the others previously mentioned: A Little Priest (trust me, jokes about cannibalism just weren't done then either and to a lilting waltz yet), Everything's Coming Up Roses (when, if well acted, you're shocked to realize Rose isn't just ruthless but deranged), Sunday in the Park, Before the Parade Passes By (no shocks but just such a great song and so much fun in Gower Champion's staging).
A Weekend in the Country.
Oklahoma's revolutionary dream ballet, which so brilliantly explored the darker themes of the show. Rodgers and Hammerstein had originally envisioned a Circus Ballet until Agnes de Mille got her hands on it.
Dr. Crippen from One Touch of Venus. Not as good as some of the others mentioned, perhaps, but an absolute favorite of mine. Also the first act finales of Weill's 3PO and Mahagonny, although I guess the latter is more properly considered an opera.
How to Succeed with its mock melodrama and musical quotations from Rachmaninoff.
And the first act finale of Friml's Rose-Marie. Again, not the greatest but a personal favorite.
Almost all the Gilbert & Sullivan first act finales are absolutely terrific but I realize they are an acquired taste today. And they can properly be considered Broadway shows as nearly all had their US debuts in the New York theater district of the time shortly after the originals opened in London and all the most popular ones had multiple revivals on modern Broadway itself during the 20th century.
Usually it's performed with just one act, but I've heard of productions of Assassins that end after the Ballad of Guiteau, and I've heard that some productions just leave his body hanging on the stage during intermission for an eeiry effect.
It's not my favorite show ever, nor did it have a healthy life on Broadway... but my immediate response to this question is the Act One finale of The Last Ship. I honestly don't even know the title of the song because the show wasn't my cup of tea, but the way they ended that first act has stayed with me ever since.
Wicked's act one finale is stupendous. My 10+ times over the years still leaves me breathless.
I very much enjoy The Great Comet's act one finale. And to add to it, the siren to start up act two.
Im sure I've got more but these are on the tip of my tongue.
A personal favorite of mine is the tap dancing Act One finale of Anything Goes. When my mother saw the 1987 LuPone revival At the Vivian Beaumont, she went upstairs to the courtyard/fountain area and promptly left, thinking the show was over! She later said to me that the show was wonderful, but so short.
Otherwise, Wicked, Baby, Dreamgirls, Miss Saigon. I like the ways Phantom of the Opera and Urinetown end - if not necessarily the musical numbers themselves.