Due to its associations with the series, This Troper gets warm fuzzies whenever she listens to the song "Could it Be?" It represents what the Kim/Ron ship had been working towards from the beginning, and anyone who's ever found love in an odd situation can totally relate.
While this troper imagines most of the 'aww' in the Kim Possible movie "So The Drama" comes from the final dance, this troper always felt that it came about ten minutes earlier when Ron and Kim wake up tied up, and Kim gets a major downer on the fact that she was fooled, and Ron pulls her right back out of it.
And of course there's The Scene from "So The Drama" when Kim is about to give up after discovering that Eric was working for Drakken, resulting in Kim and Ron becoming Drakken's prisoners;
Kim: Drakken won. I should have stuck to babysitting.
Ron: Drakken didn't win, KP, he played you. And now it's payback time. And besides, there are guys out there that are better for you than Eric. Guys that are real for one thing.
Kim: Do you really think there's a guy out there for me?
Ron: Out there... in here...
Perhaps the most heartwarming part of the movie occurred when Kim and Ron shared their First Official Kiss at the end of the film.