EC
It was, more than anything else, EC’s powerful horror comics that led to uproar and US Senate hearings in the ’50s – and for years afterwards, comics were aimed more squarely at children than any time before or since.
They don’t seem so scary today, over 50 years on. The twists are often predictable and kind of repetitive when you read a lot of them, and the insistence on describing everything in captions (the panel outlines and caption lettering were produced before the artists got to start work) is wearing. Nonetheless, they had lots of terrific artists: Johnny Craig, Harvey Kurtzman, Wally Wood, Jack Davis, George Evans, Jack Kamen, Reed Crandall, Graham Ingels. Ingels was particularly strong on creepy characters and atmosphere, but the general standard was exceptional.
There have been lots of comic reprints, so you should be able to sample these easily; and if you love them there are terrific big hardback collections.
Warren
In the mid-’60s Warren started producing post-EC comics in B&W magazine format. It wasn’t long before they relied heavily on cheap foreign artists, but early on the standards were exceptional, with art by Alex Toth, Steve Ditko, Gene Colan, Gray Morrow, Jerry Grandenetti and Neal Adams plus EC alumni like Al Williamson, Angelo Torres and Reed Crandall. The stories, mostly by Archie Goodwin in the early days, were much stronger than at EC, and some of the Toth and Ditko stories are genuine masterpieces.
Old issues of Eerie and Creepy aren’t so easy to find, though they did publish later issues reprinting the best of Ditko, Toth and Adams, for instance.
Manga
Hideshi Hino has produced 150 volumes of, mostly, horror. Some of his work is wild and hilarious, though I am getting a little bored with some tropes and repeated images. My favourite, by a long way, is Junji Ito: his best works are, for me, the best horror tales ever in any medium. I like horror well enough, but it’s rare for me to be genuinely scared, to be thinking “oh fuck, no…”, to be bracing myself before turning a page. Uzumaki is a three-volume set of stories set in a town cursed or haunted by a spiral; Tomie is two volumes of tales of a beautiful but monstrous woman (some of volume 1 is weaker early work); Gyo (review by Tom Ewing) starts with a fish with legs, and escalates in extraordinary fashion. I think he’s a brilliant creator of original and horrific ideas, and I’m sure his best work will haunt me forever.
You might find some of these in libraries – I came across him when I found Uzumaki in the children’s section of one, which is a very bad idea.
Charles Burns
I must mention one wonderful American cartoonist whose work often focusses on body horror, disease and the like. His work is genuinely unsettling, and the artwork goes from beautifully precise black and white linework to absolutely hideous. Again, you might be lucky enough to find Black Hole or Skin Deep in a library.