This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / I Am Legend
Who didn't tear up during the climax of the film, especially when he tries negotiating with the infected trying to break down his door moments after he finds the cure, desperately hoping to get through to them and prove that the last three years and all his suffering haven't been in vain.
Neville: LET ME SAVE YOU!!!!
For that matter, the original climax. While there's ultimately a happy ending for everyone, the male Darkseeker's grief, fury, and sheer, broken relief are all extremely palpable. Throw in Neville's What Have I Done moment and it's powerful stuff all around.
When Sam gets infected whilst saving Neville's life and he's forced to Mercy Kill her. Not only did he lose his only companion of the last three years, but one of the last remaining links to his family at the same time.
In the book, the end of the chapter where Neville finds the dog. After spending a month trying to get the last living creature on earth other than himself to allow Neville to pet him, it finally looks like he will have a companion. It'll be easier just to read it yourself:
"You'll be all better soon," he whispered. "Real soon."
The dog looked up at him with its dulled, sick eyes and then its tongue faltered out and licked roughly and moistly across the palm of Neville's hand.
Something broke in Neville's throat. He sat there silently while tears ran slowly down his cheeks.
In a week the dog was dead.
In the movie, the aforementioned Shoot The Dog moment, and the moment Dr. Neville begs the mannequin to say hello to him. Though some found the latter Narmy.
The "Look Daddy, a butterfly," line right before Dr. Neville's demise and the death itself.
An infected mother begging for her daughter to be taken to safety.