My favourites are of girls gagged/ballgagged, with a look of apprehension in their pretty eyes. Another favourite is a baby's pacifier in her pretty little mouth.

Tied with wrists behind back or above head, with legs ALWAYS spread wide.
I don't like girl's legs tied together, after all, that is preventing access to her most sensitive parts, thus making her less vulnerable.

A collar and leash are absolutely exquisite, as is pretty and lacey white lingerie to give the slave an "innocent" aura.

I love Mistress/Femsub bondage, with a blonde domme spanking her brunette pet and humiliating her. I tend to think of brunettes as subs and blondes as doms, which I know is the reverse of how most think it.