Links to previous and following movies in a movie franchise/series.
Links to previous and following movies in a movie franchise/series. E.g. on the movie page for "Harry Potter and the Half-Blood Prince" link to "Harry Potter and the Order of the Phoenix" and "Harry Potter and the Deathly Hallows: Part 1". Personally I would put the links in the box containing runtime and other meta information.
Concerning the source for this data I can tell you that The Movie DB have "collections" which seen to contain movie series and franchises. This data is accessible through their API similar to their movie data.
When you get the movie data there is a key in the json-response called: "belongstocollection", this key should contain either a collection-id or null.
I like this idea, but if it's too complicated, I would be happy as long as I could see this information on, say, a page for the entire series that shows the titles in order. Such as in this ticket that is marked as planned: http://support.trakt.tv/forums/188762-general/suggestions/8262348-movie-sets-sequels
I love this idea. It is one of the main reasons why I use MyAnimeList a lot (besides tracking what I watch.)