Most aspects of BDSM, including: extreme rope bondage and suspension, CBT, discipline, humiliation, most types of role play especially military, prison & convent fantasies, piercings, electical torture, cross dressing...
People with a twisted sense of humour, perverted sensibilities and considerable intelligence.
The Night Porter, In the Realm of the Senses, Blue Velvet, Clockwork Orange...
Oz
Kingdom of the Wicked by Anthony Burgess, Cities of the Red Night by William Burroughs, Justine by Marquis De Sade, Filth by Irvine Welsh, Choke by Chuck Pallahnuik