So over the holidays I read "Damaged Goods," RTD's Virgin novel, and just for fun I thought I'd list all the things I'd spotted in it that he wound up using somewhere else later on:
-Working-class family named Tyler (Doctor Who series 1 and 2, Queer as Folk)
-Woman cooking a man's favourite meal then lacing it with rat poison (The Second Coming)
-New York as the template for all future megacities (Doctor Who-- New Earth, Gridlock)
-Exploration of gay issues, particularly as pertains to different generations of gay men's experiences of sexuality (Queer as Folk)
-Housing estate (Doctor Who series 1)
-Future human whom 20th-century humans assume to be gay, but his sexuality's a bit more complicated than that (Doctor Who, Torchwood)
-War between Time Lords and someone else having consequences for ordinary humans (Doctor Who, particularly series 1)
-UNIT namecheck (Doctor Who: Aliens of London)
-A mother who makes, effectively, a deal with the devil to help her children (Doctor Who series 3)
-Bad guy driven by incessant sound in his/her mind (Doctor Who: Utopia, The Sound of Drums, etc.)
-Zombies animated by amorphous alien (Doctor Who: The Long Game)
-Reciting numbers to thwart a transdimensional alien weapon (Doctor Who: The Shakespeare Code, which wasn't his, but it's interesting that it turns up there)
Will edit this post as I notice others.