The ending when B-4 at first couldn't understand why his brother Data sacrificed himself to save Picard. And it seemed that all of Data's Tinkering, may have failed to change B4, until he starts singing the first line of Blue Skies. A song Data sang to Riker during the wedding reception.
The novelization of the film features a very bittersweet moment of heartwarming when Data dies. Just before he destroys the Thalaron Matrix, Data accesses every single memory he has of his friends on the Enterprise, and experiences them all as he's vaporized.
"You've earned a friend in the Romulan Empire. The first of many, I hope."
Worf, of all people, saying that "The Romulans... fought with honor."note His tone says, "These guys don't."
I always saw that more as the Fantastic Racism between Klingons and Romulans coming out. His family was killed by Romulans, and he spent a good chunk of his life in dishonor for it. Klingons in general view the Romulans as devious tricksters and not true warriors. Worf had just witnessed two warbirds charge headfirst into battle, not even bothering to use their cloaking devices... and noticed that even a Romulan can be an honorable warrior.
Picard and Riker's final scene together:
Riker: Serving with you has been an honor. Picard: The honor was mine... Captain.
Data manages to convey this to Geordi without saying a word before jumping onto Nemesis
The entire wedding ceremony is one big CMOH
This exchange between Picard and Commander Donatra
Picard: Commander, when this is over I owe you a drink