i don't include guro in this list cause its all by nature sick...
also uzumaki is less disturbing than other things by the same author.
he also wrote a series called Gyo that was about mutant leg machines that attach to your body and force it(your body) to produce gas till you bloat like a balloon and rot away.
quick synopsis of uzumaki
Cthulu decides to have a fun time with a group of japanese people, and tortures them through various means eventually using them to add additions to his summer home underneath the city.
Because seriously, by the end of uzumaki you see the castle and know cthulu is sitting somewhere going "Good, good" and rubbing his hands(claws?) together