Spider-Man 3 may be a fairly polarizing film, but damn if everyone didn't well up a bit at the "Birth Of Sandman" scene. Watching Sandman at one moment barely able to stand up to forming a full body with steely determination after just one look at his daughter gets this troper everytime. The beautiful musical score and jaw-dropping visuals (When you can get a pile of sand to be on both the verge of tears and have a look of absolute determination, you're doing something right) only adds to it.
After Peter has shed himself of the alien symbiote and sits alone depressed in his apartment, Aunt May visits Peter to see how things have gone between her nephew and his fiance and asks if he's proposed to her yet. Peter tells his aunt that he's not ready for marriage because he had hurt Mary Jane badly and returns the proposal ring Aunt May gave him earlier in the movie, much to Aunt May's shock. In response, Aunt May replies by saying that Peter should forgive himself and that Aunt May believes Peter will do the right thing because she knows he's a good person and she knows he will find a way to make things right again and to give it time. This scene also serves as a Tear Jerker moment.
Aunt May: Well, you start by doing the hardest thing: You forgive yourself. I believe in you, Peter. You're a good person. And I know you'll find a way to put it right... in time.
The ending, where Peter and Mary Jane get back together again. Ever since his childhood, Peter wanted to be with Mary Jane, and being Spider-Man meant that it was all but impossible. Yet, Peter has finally managed to balance his personal life and his life as a superhero, conquered his dark side, made peace with his past by forgiving Sandman, and finally, after all he's gone through, he can spend his life with the woman he loves. The series began with him wanting to be with Mary Jane, and it ends with the two of them together.
Even more than that: they've both just lost their mutual best friend and put each other through hell, but he comes back to her, and there's the implicit recognition when she takes his hand to dance with her that he won't let her suffer alone, and they'll work through their issues together. Bottom line: when all is said and done, they love each other. Especially cathartic since this troper felt this movie had more emotional trials than the others.
The novelization features the original ending for the film. Harry and Peter are trying to defeat Sandman and Venom and even with the added help are having trouble. Then Sandman's daughter and ex-wife show up and beg Flint to stop, with his daughter telling him that he isn't a bad person. Flint returns to his human form but Venom begins to go on a rampage. Peter tells Flint to run and get his family out of there and the three leave.
Mr. Ditkovich, Peter's apartment landlord, brushing off the angry outburst Peter (who was under the symbiote's influence) just dealt on him, assuring his daughter that Peter is a good boy, and then quickly forgiving Peter later on when the latter comes to apologize. Furthermore, Mr. Ditkovich lends Peter some romantic advice upon learning that Peter plans to propose to Mary Jane. Heartwarming in retrospect, when one considers his portrayal from the previous film.
While it's a bit sad considering how Peter is stringing her along and she's lapping up the attention she's getting from him, it's sweet that Ursula is catering to Peter's every whim and stuffing him with an endless buffet of her homemade cookies.
Bruce Campbell's cameo is both funny and heartwarming, in contrast to his other characters who either mock or impede Peter he is instead thrilled at the idea of Peter proposing to MJ at his restaurant and deeply honored to be asked for his help in the matter.
In perhaps the best of Stan Lee's cameos (and Stan the Man's personal favourite), he muses on the impact of Spider-Man in fictional New York to Peter Parker. It's easy to interpret it as Stan talking about the greatest lesson comic book superheroes (particularly Spider-Man) try to teach their readers:
Stan Lee: You know, I guess one person really can make a difference. 'Nuff said.