The Hobbit
From Tardis Wiki, the free Doctor Who reference
The Hobbit was, according to an old man at Bernice Summerfield and Jason Kane's wedding in Cheldon Bonniface on 24 April 2010, "not so much a book, more a way of life." When he gave the newlyweds a signed first-edition copy of the novel, he told them it changed his life beyond recognition. (PROSE: Happy Endings)
Benny thought Gully looked like a character from The Hobbit. (PROSE: Digging up the Past)
Behind the scenes
The Hobbit is Tolkien's prequel to The Lord of the Rings.
Sylvester McCoy played Radagast the Brown in Peter Jackson's film adaptation of The Hobbit. This fact was often referenced in The Five(ish) Doctors Reboot.