I think some of the best horror films are the really cheesy ones, almost, ones that make you laugh at the ludicrous nature of it all, or are just meant to be funny, and these are some of those..
The Nightmare before Christmas I've had multiple discussions with friends about whether this is a a halloween film or a christmas film - in my head, it goes with halloween so perfectly, I don't see another place for it. I love the songs, and I think everyone knows it, but it deserves a mention.
Cabin in the Woods I think this is supposed to be in the actual horror challenge, but the end few scenes border on such hilarity for me, it has to be in here. Post-watching, I would go and look up some of the monsters.
Teeth Get your girlfriends together and watch this - and enjoy how hilarious it is. It's based on the premise of vagina dentata.. teeth in the vagina. I like the idea of it being an empowering women thing, but the concept is actually just hilarious, so you might as well enjoy it, it has a dark humour and I think it's a little bit underrated.
Shaun of the Dead Everyone loves a zombie film, and I think this is one of the best that doesn't take itself too seriously (because lets face it, zombies aren't serious).
Rocky Horror Picture ShowJust because. I really want to dress up and go see it somewhere. I know a few people that haven't seen this yet and I really do wonder why.
Honorable mention: Coraline. It's a kids film about an girl who discovers her 'other' family who is trying to lure her away and sews buttons on their eyes. It's not as scary a film as the book - the book is written by Neil Gaiman and genuinely terrified me when I read it a few years back (I wasn't even a kid!).