I almost wiped this from memory
I'm so sorry
Sengoku Rance and Monster Girl Quest are pretty great (Sengoku Rance in particular for the gameplay), though most Rance games are worth looking into. Tsukihime and Fate/Stay Night are well-known, though the sex is mostly for the hilarity than anything else. Saya no Uta is infamous mostly for the horror and, hey, Nitroplus.
You might want to make sure you're alone before playing these.
Thanks. I recognize a few names ther. Saya no Uta I know from Gen Urobuchi fame.
And that goes without saying
If we're going that route, this is an important question.What about dragons and dolphins?