This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Desperate Housewives
Way back in season 1. Bree, polishing her silverware, receives a call from the hospital informing her that her husband, Rex, has died. Bree takes the news calmly, and continues to polish the silverware. When she's finally finished, she sets it all down, sits at the kitchen table, and starts bawling. This is after she and Rex had been estranged for most of the season, and earlier in the episode, they were starting to finally reconcile.
Gabrielle breaking down into tears and screaming while Lily is brought away by her biological mother.
"Bang". Especially Lynette promising to take care of Nora's daughter, then yelling at Carolyn for shooting Nora in spite of the fact that up until this point, Lynette and Nora had been enemies and Mary Alice's end narration: "This was the last time Lynette would dream of me. And for that, I am glad."
"Come Play Wiz Me". Ian saying goodbye to his dying wife on the phone while Susan holds the phone to her ear.
"Now I Know, Don't Be Scared" has two tear jerkers:
When Danielle, after being portrayed as a typical selfish bratty teenager (and having stated earlier in the episode she hated the baby because all it did was make her fat), holds her newborn son for the first time, and then decides to let her mother raise him because "it's best for everybody. Especially him." This becomes all the more tear jerking when you know what's going to happen during the time jump (see Season 5).
At the end of the episode, when Lynette is told she is cancer-free. While her husband and mother go off to celebrate, she stands there in shock as melancholic music slowly begins to play in the background. She goes outside into the backyard and watches the stars, taking in a deep breath with a satisfied smile on her face, realizing she has her whole life ahead of her. As if that's not bad enough, she sees the possum she had been bent on killing the entire episode lying dead on the ground. She bends down and sobs out "I'm sorry!"
The end of the tornado episode, when Lynette thinks her family died in the tornado.
In the season five premiere, after seeing Bree as being ultra-dominant and overall bitchy, we learn why: During the five-year jump, Danielle came to take back her son, and she does so viciously, knowing full well that by this time Bree has bonded with the boy enough to consider him her own son. When Bree tries to tell her that the boy is all she has, she harshly responds, "Well, you're just going to have to find something else."
The one-hundredth episode is about a handyman named Eli dying and the housewives looking back on how he touched their lives in various ways. Mary Alice's flashback in particular was what got to this troper: Eli helped Mary Alice repair a vase when she first moved on. In a second flashback, she gives Eli the same vase and tells him to go. In her hands, we see her unfolding the blackmail note she got that caused her to commit suicide in the very first episode. It is then revealed her suicide was what caused Eli to try to change people's lives.
Death of Edie Britt her tribute episode is also sad, especially at the end when the housewives spread her ashes around the neighbourhood, and right before when they use one word each to describe the kind of person Edie was. Susan ends up choosing four words: "one-of-a-kind".
After saving Orson from attempting suicide, Bree gives him this answer when he asks her if she still loves him:
Bree: I lov you once.ed Can I love you again? I don't know. But I would like to recapture what we once had. How can we do that if you're not here? So I'm asking you again: Please stay.
The more recent flashback episode for the strangler on Wisteria Lane, which gives them a heartbreakingFreudian Excuse. Basically, as a little boy, his father walked out on his mother in front of him, resulting in the mother becoming an alcoholic, emotionally abusive, negligent parent who has always laughed at his dreams, put him down even when someone stepped in to help, and claiming he would never find love—all to punish him for resembling his father. Is it any wonder this person ended up the way they are?
After spending most of the season having marital problems, Tom and Lynette decide to separate.
Paul's breakdown to Susan following his decision to take Beth off of life support. The man has spent most of the series in gross opposition to Susan and her family, that him breaking down and telling her to accept Beth's kidney as a way of honoring her was a hard hitting moment.
The centerpiece of the final episode was the death of Karen McClusky.Her actress passed away only a few weeks after airing.
The flashback that explained why Bree is the Stepford Smiler she is now: when she was a little girl, her mother (implied to have found out that her husband was cheating on her) told her it's best not to let people, especially husbands, know how much you care and feel about them and their actions. Then cuts to an adult Bree telling Rex how bad she felt when she heard him proclaim that Gabrielle is the most gorgeous woman at the party they left, he brushes off her feelings and she weeps, saying "I was thinking about how right my mother was" and puts on a happy face to make cookies.
Also in the final episode, when Susan leaves the lane for the last time and she sees the ghost of Mike watching over her. Amplified as other ghosts appear to send her on her way, particularly Mary Alice appearing last on the word 'wonderful', looking serene and at peace.