Karryn's prison, it has the best implementation of a sex-fight system I've ever seen, and I'm kinda sad to see that barely any games has followed in it's footsteps.
Mentioning because of how pleasantly surprised I was by it: College Craze. There is definitely some room for improvement, but it's already really damn well done and if the art is up your alley (similar to Good Girl Gone Bad) you should give it a look. I think right now it's free but on full release (soon-ish) it won't be. a lot of different routes with a good array of different guys with nuance in their approach to an MC that is different (virgin, part of a certain club, etc). It hit the spot for story and art as well as the collectables itch because i wanted to root out all of the different CGs and storylines i could. one big thing to note: if you don't like stalking (you can reject it, but it IS a main part of the story) then it might not be the game for you.