Outlast, Amnesia: The Dark Descent (You have to add something unique for this to work, or you get the "Pewds did this first" comments).
Also, PokeMMO seems to be fairly popular, any kind of indie game can do good if you promote it right, horror games do pretty good with facecam and such.
It depends mostly on you, I love horror games, so that is what I usually play. Sometimes I do games like Castlevania or PokeMMO which are series I'am currently working on. I was doing Aarklash and it was doing really good, but I don't really like the game, so I can't have fun playing something that I don't like.