Private Life of Sherlock Holmes
I'm sure you'll all have already noticed this, but every time I watch Billy Wilder's "The Private Life of Sherlock Holmes", I realize again how much "A Scandal in Belgravia" is an adaptation of this movie rather than of "A Scandal in Bohemia". So many connections there and some scenes from ASiB (like the final scene) suddenly make so much more sense when you keep this movie in mind. (And I'm convinced saving Irene at the end of ASiB is Moffat's private "fix-it" for "Private Life"! :-P)