The official website. It fills you in on what happens to the characters after Donnie's sacrifice.
Although I'm aware of Kelly's explanations for what's going on (tangent universe would have destroyed universe if Donnie didn't act, manipulated dead agents of God, blah, blah, blah), I prefer the simple one you can discern from the film itself. Donnie sacrificed himself so that Gretchen, his mom, and his sister could live. I don't need to know how he did it, and the more involved the explanation gets, the less interesting the movie gets. It's why I'm perfectly satisfied having only seen the original version of the film.
Mad World is awesome. As is the @##%! for Fears school intro montage.













