Updated: Nov 19, 2021
There are some characters whom we hated till the end, like Umbridge. But there are some who turned good, and earned pity. I don't know why, but it's just so nice, to feel that these people have turned good, try it out! Let's look at the top 5 who turned good.
Most of us didn't like him in the first movie, but he turned good in the end.
One proof for this was, (It isn't there in the book or movie) during Fred's funeral, Draco lingered in the back, and when he thought everyone left, he stayed back, truly sorry for the part he played in Fred's death. He would never admit that he was there, and George (who was the one who stayed back) would never tell anyone that he saw Draco crying, and apologizing to Fred's headstone. He considered it as an apology to him when Draco apologized to Fred, and so didn't tell anyone.
He also supported Harry, when they were caught by Bellatrix. He lied that it wasn't Harry. He definitely turned good. Don't judge him on the choices he made, when you don't know the options he had.
Narcissa was siding with Voldemort, and so we obviously considered her bad. But when she went near Harry to check weather he was dead, and told the Dark Lord that he was, even while he wasn't, we knew that she switched sides.
As it said in the books, she didn't care if she betrayed Voldemort, she just wanted Draco safe.
Well, Kreacher wasn't ever actually bad, in a way he was actually loyal - to only Regulus Black, though. He found Sirius and his friends horrible, till Harry gifted him the locket of Regulus Black's, and asked him to capture the man who stole the real locket. One sad part was when Hermione accidently made Yaxley - a death eater into a secret keeper. She said "Kreacher would have cooked it so hard for us, only to find Yaxley with other death eaters."
Petunia and Dudley Dursley When Harry was finally leaving from Privet Drive forever, Dudley admitted that Harry wasn't a "waste of space" after all, and coming from Dudley, that's awesome. Petunia admitted too, that she didn't really hate Harry, she wanted what all of us want, go to Hogwarts, She was jealous of Lily, and took it out on Harry.
Peter Pettigrew He didn't actually turn good, but he knew when he made a mistake, and he knowingly paid for it by killing himself. In the Deathly Hallows, when Harry, Ron and others were trapped in the cellar, and Peter was sent to find them, Harry reminded him that he saved his life in the shrieking shack. (Prisoner of Azkaban) He put his own metal hand to his neck and chocked himself to death.
These are all I could find. Let me know if there are any I missed by putting it in the comments.