Here are some things I've wanted, and I'm open to any variations on all of them. As for ons and offs, I'm willing to take things as far as you are. PM me or post here if you're interested.
1: Big Sister
A boy is tormented by his older (possibly step-) sister. She forced him to crossdress, and blackmailed him with the photos. Now he has to do whatever she says. Incest, crossdressing, non-con, dub-con, pegging, humiliation.
2: Fresh Blood
A female vampire takes interest in a young man who just moved into town with his wife. She seduces him, but he tries to stay faithful. Possibly mind-control on him or his wife. Possibly set in early 20th century. Bondage, bloodplay, non-con, dub-con, persuasion, possible mind-control.
A guy is forced to attend an all girl's school and live in the dormitory. He become fast friends with a girl in his class, and soon falls in love with her. Little does he know she feels the same way. Awkwardness ensues as they worry about how their love will effect their friendship. He struggles with possibly revealing his identity, and she worries about being a lesbian. Crossdressing, teasing, accidental stimulation.
A kidnapper captures and tortures a victim. This could go either way, F/m or M/f. Bondage, non-con, blood, minor injury, possibly all they up to mutilation and dismemberment.
5:From Dancing to Dueling
Bruce Wayne and Selina Kyle don't know that the other has a secret identity, namely Batman and Catwoman. While Bruce and Selina are getting together during the day, their alter-egos are dueling under the stars. Who will find out first, and what will it do to their relationship? Rough sex, minor injury, light bondage, and possibly more later in the story.
6: My Little Angel
A genius inventor spends most of his time in his lab, to the detriment of the relationship he has with his only daughter. One day, she dies in a horrific accident while he watched, unable to do anything. Distraught, he builds a robotic replica of her, identical in every detail, programmed to love him unconditionally. Pseudo-incest, older male and younger female.
7: Don't Stand So Close to Me
Based on the Police song of the same name. A teacher is crushed on by one of his female students. He feels awkward, unsure about what to do about her advances. Stalking, dub-con.
8: Nobody Likes a Wet Cat
A single guy living alone in an apartment is walking home one day in the rain, when he finds a box with "Free to a good home" written on it. Inside he finds the most pathetic looking cat he had ever seen. He takes it home and feeds and drys it. The next morning he wakes up to find that it was actually a catgirl! She is very cat-like (cleaning, yowling, sometimes standoffish, sometimes affectionate) and can transform back and forth between a cat and a catgirl at will. She knows next to nothing about being human, and he has to teach her what is and isn't appropriate.
9: Bonnie and Clyde
We're a pair of outlaws, robbing banks, killing people, running from the law and completely in love with each other and our lifestyle. We don't do it for the money, we do it for the thrill. Can be either modern, or classic (20s, 30s), or even a different time period.
10: Bride of Dracula
A male vampire captures and brainwashes a human woman to make his eternal bride. During the course, she is turned into a slave to both him and her sexual desires. Either modern or turn of the 20th century. Bloodplay, degradation, begging, slavery.
11: Futanari Friend
A guy finds out that one of his closest friends is actually a futanari (completely female + penis) (Either she tells him or he finds out accidentally). She reveals that he is the only person who knows. She also tells him that she has never had a boyfriend or had sex, for obvious reasons. They decide to have sex, and learn about themselves and each other. Futanari, virginity, (probably) excessive semen, (probably) pegging.