Haha, where to start? ;p
(All of this refer to women as subs, either to men or other women. No interest in sub men.)
-Anything that makes a girl feel like a filthy slut, yet it makes her cunt drip and throb so much that she can't help wanting it. Girls that enjoy feeling like worthless whores.
-Consent. Or dubcon / semicon. *Not* noncon. For fantasy purposes I do like subsluts who are caught between "sanity" and their depraved/humiliating desires. Wanting it, but hating herself for wanting it. Kinda goes with above.
In more specific terms...
Humiliation
Snuff
Breeding
Ass to Mouth
Objectification
Orgasm Denial
Mutilation
Dirty talk
Piss
General pain and abuse
Stuff I'm not into:
Scat
Incest
Ageplay