Like many others, I enjoyed 28 Days Later quite a bit. I didn't care for (most of) the sequel, tho.
Dagon is one of my favorite movies, although it's really not that good.
Alien is gold, The Host is pretty good, the original Night of the Living Dead is awesome.. I liked the first Terminator movie, which is arguably horror-ish. Oh, and Predator. Creepshow is a good fun time. Rosemary's Baby.. Oni Baba.. Poltergeist.. Pumpkinhead.. Rawhead Rex.. The Exorcist.. The Omen.. and way too much more. Oh!.. and I loved the Rob Zombie movies that came out a while back.. uh, Devil's Rejects and the one before it. Haven't seen his Halloween remakes yet, tho. I freakin' love horror movies, whether it's gore or exploitation or psychological horror.. it's all good.