"Lemonade" from Babes In Toyland (I really don't know which version of the show though, but not the original, since I don't think "Lemonade" was in that). It was my first regional production musical (operetta, but not really) I saw.
Though if we go more professionally, "The Heat Is On In Saigon" from the second national tour of Miss Saigon in Seattle.
And if we go by first Broadway show on Broadway, "Promises, Promises" from the recent revival. It's taken me about 17 years to get from my very first musical experience to actually going to Broadway.
Xanadu! Can't cry on cue!