The Thing is an absolute classic, gotta check that out if you haven't seen it. For a less well know one: Annihilation. I haven't really seen anything else like it - it kind of starts with regular, competently done sci-fi stuff and gets into what I'd call psychedelic horror. It was cool as shit but disturbing in a way that I don't come across much in movies. I guess Eraserhead would be the closest thing I've seen in terms of vibes.

Edit: also, Cargo, on Netflix. Not quite a horror movie but it is a zombie movie, so close enough? It rocks though.