Asha reaffirming her Undying Loyalty to Shepard by rejoining her crew on Horizon. She doesn't even hesitate.
Especially since the "Virmire Survivor Lecture," is one of the most hated moments in Mass Effect because of all the stupidity it brings up, so seeing this utterly subverted is a rather nice touch.
The entirety of chapter 81: Liara and Shepard's wedding. It's a wonderful culmination to their relationship and the character development both have undergone, and a moment of light-heartedness as the Reaper war continues. Moreover, it also adapts the latter half of the Mass Effect 3 Citadel DLC, and lets the Normandy crew relax and party for a short while despite the galaxy falling apart around them.