I would like to shoot out some basic VN plot ideas and maybe that will inspire some of us to manipulate them into something more VIP or entertaining:

Guy goes to school, harem, some sort of drama
Medieval war story with warrior/princess women, think UnderwaterRayRomano
Medieval RPG-type story
Strange convoluted magic-related story (ala Fate/Stay Night)
A bunch of maids serve you or you're a servant