Any co-op (2 player - 4 player) suggestions?

I am looking for some fun co-op games. Add-on or otherwise. Typically we like the "horror"-ish type of co-op. Creepy atmospheres, maybe a couple pop-up scares etc.

Games I've already finished: Dead Island, Dead Horde, Portal 2, F.E.A.R 3, Resident Evil 5&6, Killing Floor, Torchlight 2, Trine 2, Borderlands 1&2 (and most DLCs)

If I get one of the suggestions and really enjoy it, I'll purchase an extra copy to make a giveaway; gotta share good games!

Thank you for any suggestions =). Also my apologies if this thread has been made a million times, I'm still a bit new to Steam Gifts.