There are too many I love for various reasons. Some of my favorites are:
Cannibal Holocaust - What's not to love about this film. I admit my soft spot for Italian cannibal flicks and Italian cinema in general but this is one of the most brutally beautiful films of all time. The story and acting are great. Deodato and D'Offizi's shots of the jungle were amazing and gorgeous and Riz Ortolani soundtrack is both haunting and beautiful at the same time. Deodato's message is just as poignant and relevant as it was when the film was made. Of course the animal deaths are nasty...Particularly the coatimundi and turtle...But I've seen worse.
Night of the Living Dead - The best film ever made. No explanation needed. The rest of Romero's dead films are incredible too.
Dead Alive / Brain Dead - Completely over the top gore and slapstick comedy combined amazing gross out and WTF moments. Like the priest kicking *** in the name of the lord, the zombies doing it and having a baby zombie, the rockabilly zombies guts coming to life, the mothers puss shooting in the guys pudding...I could go on forever.
The Exorcist - Who doesn't love The Exorcist.
August Underground - The fist time I saw it I was mesmerised at the oddity and reality of the film. The second film Mordum makes my all time gross out films list. The scenes of Maggot doing certain things to the corpses will forever be stuck in my head.
Murder Set Pieces (The directors cut, not the Lion's Gate crap cut.) - The best slasher of all time hands down!
Aftermath - Crazy subject matter with a twisted ending. Beautiful yet extremely brutal and disturbing.
Bad Biology - As a huge Frank Henenlotter and R.A. the Rugged Man fan I love this film. It has to be one of the weirdest films I've ever seen.
I could go on all day and night. Horror is my main genre of film and used to spend a great deal of time posting on horror and Italian cinema forums. I have a vast rare horror film collection and have seen just about everything good or bad.