This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Attack of the Clones
The opening where Padme's ship blows up, and we think that she has been killed from the impact. Then the pilot takes off her helmet, revealing herself as the real Padme. It doesn't lessen her anguish as she begs for her bodyguard Corde to stay with her. Corde merely says Sorry That I'm Dying before closing her eyes, and Padme stares with grief and horror. It's also the first time onscreen that we see the sacrifices that the bodyguards have to make by impersonating the queen.
A Cry for the Devil moment: the female assassin gets injured and captured, and as a result Obi-Wan and Anakin interrogate her politely. They don't use any Jedi Mind tricks, just Politeness Judo, seeing that she's incapacitated, and then she gets killed in front of them as she's about to reveal her employer's name.
The end where a 10-year-old Boba Fett is seen picking up his father's helmet.
Jango's only fee for donating his DNA was having an unaltered clone. The novelization has Obi-Wan note that perhaps Jango only wanteda son, rather than someone to replace him.
If you read the "Young Boba Fett" books, he (Boba) mentions that he thought that Padme Amidala was exactly how he'd imagined his mother to be. The sight of him as such a young, innocent, idealistic child, and knowing what will happen to him in the future...
Shmi Skywalker's death. She's been captured by Tusken Raiders, tortured to near death, and dies in the hands of her son, just managing to get out "I... love..." before dying. And people wonder why Anakin's so messed up. You could totally understand why Anakin would do what he did next (even though it was horrible itself) after having his mother die in his arms like that. Anakin's utterly broken plea of "Stay with me, mom." - complete with trembling jaw and watering eyes... Anyone who has ever lost a parent will know his sorrow.
But that doesn't forgive what he then does. He kills the entire tribe of Tuskens. And not just the men, but the women and the children as well. Which leads to a horrific My God, What Have I Done?.
"Across The Stars." The credits version even more so, which segues into a mournful rendition of Anakin's theme from Phantom Menace before ending with the ominous bass strains of "the Imperial March."
Obi-Wan, taken captive by the Seperatists, is confronted with Count Dooku who tells him that he regrets Qui-Gon's death and would have liked them to work together. Obi-Wan retorts that Qui-Gon would never have joined up with Dooku. His tone and facial expression show that he's furious and that even after ten years the loss still hurts like hell. So much for no attachments, ey?
In the novelization, while visiting Padme's parents Anakin finds a photograph of Padme doing intergalactic community service. She tells him she was helping to save civilians from a planet whose sun was dying, and that they "were" wonderful. When Anakin asks, "Were?" she soberly tells him that the civilians couldn't live off their planet, meaning her work was All for Nothing. Yet she kept doing that work, despite the losses, until she became queen.
Also from the novelization, Padme notes that the Separatists are an Ungrateful Bastard lot for how she plead for mercy on their behalf, despite the fact that they invaded her planet and enslaved her people, and to return the favor they've tried to kill her. It doesn't even make sense from a Pragmatic Villainy standpoint to eliminate an opponent that prefers clemency to violence. Granted, Palpatine was manipulating them to assassinate Padme since she opposes his rapid rise to power, and probably played on the Separatists' emotions.