Eyes without a Face (1962) - terrific - both effectively lyrical and horrific
Lyrical as in Billy Idol lyrics?
Blue Velvet - only if you haven't seen it or know any of the twists - watch it knowing nothing
I'm not going to say much about this except to say that it's not really horror at all. It's disturbing, no question, but it's much more surrealistic, as most of David Lynch's stuff is. It's sort of noir meets surrealism, in my opinion. An excellent and disturbing film, but not truly what I'd consider horror.
Bone Tomahawk - watch it. Then try to unwatch it.
I just watched this and...it's...odd. It's like a Quentin Tarantino film, what with all the quirky dialogue and slow pacing, but by the time you reach the actual horrific stuff it's pretty freakin' gruesome. It'll stay with you, no question. I would say that, if you know what to expect going in (in terms of how gruesome it is), it's manageable, although you'll still want to look away at parts. Actually, "gruesome" isn't quite the word. It's truly savage in the violence it depicts.
Anyway, moving on.
A few other suggestions:
- Night of the Creeps, followed immediately thereafter by Slither. Fred Dekker directed the original. James Gunn directed the new one. Very similar stories, though.
- April Fools' Day. I always loved this horror film, if only because, as a slasher film, it was one of the original "rule breaking" films. It's definitely goofy, but fun.
- John Carpenter's "Apocalypse Trilogy." These films aren't truly a trilogy in the sense of linked narratives, but they are connected by thematic "end of the world" qualities. Kinda like the Cornetto Trilogy, only not remotely funny. The films are: The Thing (1982) -- see this if only for the amazing-for-their-time f/x; Prince of Darkness (1987) -- kind of like a Hammer/Quatermass story in its weirdness; In the Mouth of Madness (1994) -- Carpenter does Lovecraft. A favorite of mine.
- Lord of Illusions. This isn't truly horrific, but it's like film noir mixed with horror elements. I really, really love this film, although I'm not really a huge Clive Barker fan, or at least not a fan of most of his works as adapted to the screen.
- Nightbreed. ....with the exception of Nightbreed, that is. I watched the original version, and the restored director's cut recently, and I actually kinda prefer the original. The stuff in the director's cut is interesting, but the original is, I guess, what I bonded with. Again, not exactly horrific or scary, but has horror elements.
- Tremors -- the original. It's basically just a B-movie, but it's lots of fun.