Lelouch's letter to Nunnally on her birthday in Chapter 61.
Abigail comforting Lelouch in the same chapter...yes, that Abigail.
C.C. comforting Lelouch after a terrible nightmare and using her Code to make sure he had good dreams that same night....at the cost of a good night's sleep for her.
Cornelia and Euphemia reuniting after the Hotel Hijacking...also doubles as a Tear Jerker, because we're reading this sweet moment through Lelouch's perspective, who looks in envy, thinking of his own little sister that he's been separated from for months.
Lelouch and Suzaku (and Jeremiah) reuniting with Nunnally...it makes you get warm fuzzies AND tear up! Nunnally and Lelouch REALLY needed this.
Also heartwarming because it also shows that Lelouch finally trusts Jeremiah.
Well even before that you could tell Lelouch he trusted Jeremiah. After Jeremiah saved Euphy's life, Lelouch thanked him, addressed our favorite Orange as "My Knight" (something he only has called Suzaku but not Jeremiah) and allowed Jeremiah to address Lelouch by his first name, instead of titles. This whole moment was a crowning moment of heartwarming all on it's own. Allowing Jeremiah to see Nunnally was the final piece of this wonderful puzzle showing us that Lelouch has come to trust Jeremiah! :)
The whole moment between Lelouch and Euphy after Jeremiah saved her from the terrorist, was both this and a Tear Jerker. Euphy this whole course of the story was saddened because she doesn't know the Lelouch she once knew. She didn't feel like she was someone he could fully trust. However this moment proved to Euphy that Lelouch still cares about her and has a soft spot for his half-sister. The whole thing was touching. This troper actually teared up with a big fat smile on her face.
In the most recent chapter (77), Lelouch realizes how harsh he's been with Abigail in the past, and seeing she's been through alot being kidnapped by Mao, actually comforts her. The whole situation was very sweet. The two actually begin to act like a true husband and wife.