Devilman - 53 chapters in 5 volumes. It was the main inspiration behind such manga as Berserk and Kiseijuu.
Saint Seiya - 110 chapters in 28 volumes. A good series if you're interested in Greek Mythology, though it'd require buying some volumes, as there's no English scans for volumes 12-18.
JoJo's Bizarre Adventure Part 1 - 44 chapters in 4.5 volumes, or 3 if going by the JoJonium edition. Of course, the overall series is far longer, but you can use this and part 2, or the 2012 anime, as a taster into the series.
Kongo Bancho - 114 chapters in 12 volumes. Made by the same person who created Nanatsu no Taizai, which must've you have gotten into.
Koroshiya Ichi - 101 chapters in 10 volumes. A pretty good psychological series that some of you will be aware of from it's movie adaptation, "Ichi the Killer".
Gou-Dere Sora Nagihara - 24 chapters in 4 volumes. One of the few series where I consider the humour to be near Gintama tier hilarity.