The scene when Troy appears on Gabriella's balcony in 1.
The looks on Mr Bolton and Mrs Montez's faces when they see Troy and Gabriella singing on stage.
Gabriella coming back and doing a duet with Troy after having left in "Every Day."
Gabriella teaching Troy how to waltz "Can I Have This Dance" in 3 and then telling him 'yes' she'll go to the prom with him in every language known to man.
Bonus points for their dance being on the rooftop garden where they had their secret meeting in the first film.
The Wildcats reactions when Gabriella returns at the end of 3: Even though she screwed up and left, they're all just happy she's back. Pretty heartwarming for a character who started with no real friends.
Troy's graduation speech in 3. Tear Jerker, too, because damn, Zefron did it well.
Here's one involving the cast: They all stayed friends since the films, and when Monique Coleman was on Dancing With The Stars, Ashley Tisdale, Corbin Bleu, and Lucas Grabeel all showed up, brandishing pom-poms in East High colors to cheer for her.