Back to the Future
From Tardis Wiki, the free Doctor Who reference
Back to the Future is a popular 80s film
Martha Jones didn't see any threat from the Carrionites because she knew that the world didn't end in 1599 as she was living proof. However the Doctor referenced this movie when he told her about how Michael J. Fox travelled back in time, did something that almost erased him from existence in the past. (DW: The Shakespeare Code)
Behind the Scenes
Christopher Lloyd, who played time travelling Doctor Emmett Brown in the movie and its two sequels, was almost cast as the Master in the 1996 Doctor Who: TV Movie. However, Universal (the studio which was financing the movie and also financed the trilogy) baulked at the pay he was asking for.
