I spent most of my life not watching much in the way of horror, because it wasn't a genre I found really interesting. The past couple of years have been a horror period for me, but I can't put my finger on why I keep coming back. Horror films are never successful. I can laugh at a comedy, I can get emotionally invested in a drama... I can't get scared by a horror movie. I really like the idea of a scary movie but I haven't found one yet.
Anyway, I don't know what you have and haven't seen, so this is just a random sampling of stuff I've seen fairly recently, mostly ignoring the obvious staple-type things, especially when DiF has done them. Like The Shining or The Fly. These are not in any particular order.
The Cabinet of Dr. Caligari - Goes well with Nosferatu.
Re-Animator - Super fun horror-comedy. Jeffrey Combs at his best.
We Are What We Are - Super pretentious and will have you in hysterics during the climax.
The Wicker Man - The Christopher Lee one, not the fucking Nic Cage one. Really bizarre, atmospheric film that's genuinely unsettling.
The Innkeepers - Slow burn haunted house that does a lot right and an equal amount wrong. Sara Paxton is charming and almost enough to carry the film.
The Conjuring - Nice subtle poltergeist movie for most of the run-time. Not perfect, but well-crafted with a strong cast.
Black Death - Interesting for being a medieval horror movie. Not entirely successful, but pretty engrossing.
Pumpkinhead - Full-on eighties monster movie. Great creature, directed by Stan Winston himself. Stars Lance Henriksen, who does anything but phone it in.
The Others - Well-acted, well-shot, solidly twisty plot.
Any Evil Dead movie - 2 is the best for comedy value. 1 is interesting for the way it overcomes budgetary issues. Remake is fascinating to watch when you have the context of the other two, even if it isn't the strongest example of the genre. Avoid Army of Darkness at all costs.
The Perfect Host - Watch it for David Hyde Pierce. He's incredible in this movie.
Nightmare on Elm Street - The first one, the remake, and Wes Craven's weird meta commentary on the franchise, New Nightmare, are all worth checking out. I can't vouch for the sequels, I only saw the second one and it was miserable.
Spider - More Cronenberg for you. Ralph Fiennes is phenomenal in this.
Below - Trey recommended this on Pitch Black, and it is really good. Haunted house in a submarine directed by David Twohy. Starring Olivia Williams, who I have such a crush on.
Guess that's probably enough for now. Also, Manhunter doesn't really count as horror, I don't think. It's more of a thriller.