Dewey's marriage proposal to Gale at the end of Scream 3. Your heart is warmed when you see those get two get together, after what they went through.
Minor one in the end of two. After spending the entire film still being uncomfortable around Cotton despite knowing he didn't kill her mother, Sid praises him on National TV, allowing him to become a public hero. This is after he saved her life from Debra.
The scene in the climax of the first, after being chased by the killer Sidney finds Dewey. before it's revealed he is stabbed in the back. The smile on his face when he sees she is ok just shows why we all love Dewey so much. He gets better though.
It's ambiguous whether Cotton had any knowledge of Sidney's whereabouts or not, and if he'd tried to help, Ghostface might have still killed him. However, the fact Cotton didn't even consider trying to help Ghostface in exchange for his life is heartwarming. He kept his word about never doing anything to hurt Sidney.
Sidney's boyfriend in 2 gives her his Greek letters to protect her, indeed they do at the end of the movie she uses them to disable the killer for a moment, and she continues to wear them in 3.