While a somewhat sad moment, Kat looking down out her window at Bianca, devastated that she can't go to the prom and knowing it's all her own fault, then the following scene where she is seen walking out the door to go to the prom, beginning the segue into a Moment of Funny
And then there's Cameron, Bianca, Kat, Patrick, Mandella, and Michael meeting up at the prom. Michael dresses up as Shakespeare and gives Mandella a period dress, because he knows how much she loves Shakespeare. Cameron and Bianca get snuggly and are laughing together. Kat squees over her favorite band playing (which Patrick arranged to have happen, even though he hates their music). There's a moment where Bianca and Kat smile at each other, which is the most friendly they've been together throughout the movie. It's just so sweet overall!
Kat and her dad having a heart-to-heart as well as letting her go off to college on the other side of the country. Then, when it's revealed Mr Stratford sent Sarah Lawrence a check so Kat can attend, it becomes very sweet when Kat hugs him, considering their animosity earlier in the film.