Ill just state a few of my favorites

• Cyanide and Happiness. Going for almost 20 years,, maybe 20 years by now. Has both crude and witty humor
• MrLovenstein. Personal humor. Can be wholesome. Can be relatable. Kind of just how life is and how it works.
• Extra Fabulous. Like C&H, very crude but also somewhat surreal
• Oglaf. Sex. Lots of medieval setting sex. Sometimes not sex. Usually sex.
• XKCD. Smart people making smart jokes.

Here are some cartoonists who are likely to have collections in public libraries:

• https://en.wikipedia.org/wiki/Chris_Ware - a genius. I had to stop reading bc they were too impactful. strips, one-pagers, and longer stories, many experiments with forms. If you want "clever", this is your guy.
• https://en.wikipedia.org/wiki/Jim_Woodring - another genius, surreal cartoony style. scary thing is when they start making sense. multi-page short stories, one-pagers.
• https://en.wikipedia.org/wiki/Alison_Bechdel. literally a MacArthur-winning genius. earned acclaim for her later graphic novels, but she has an earlier strip called "Dykes to Watch out For" that has some excellent characterization and captures a moment in time that is very relevant

Cartoonists who work with longer forms, while keeping a cartoony style:

• https://en.wikipedia.org/wiki/Charles_Burns_(cartoonist) - hit or miss, but when he hits it's like a baseball bat to the face
• https://en.wikipedia.org/wiki/Daniel_Clowes - a bit overrated imho but got respect for him
• https://en.wikipedia.org/wiki/Raina_Telgemeier - does cartoons for kids, but they're great. "Drama" and her adaption of "The Babysitter's Club" are especially good
• https://en.wikipedia.org/wiki/Peter_Bagge - early stuff is very counterculture, later stuff includes some interesting biographies

Defunct but gold: Achewood; Cul de Sac; Hark! A Vagrant!; Perry Bible Fellowship (maybe still posting?)

Still putting out bangers: Nancy; Xkcd; Oglaf; Wondermark; KC Green; You’re All Just Jealous of My Jetpack

Politics: Tom the Dancing Bug; This Modern World; Kelly Comics at the Onion

Topatoco.com also has a (mostly) quality list of creators

Red Meat

Dinosaur comics

Defunct and not as witty, but Cow and Boy was very clearly inspired by Calvin & Hobbes

• Nedroid
• Questionable Content

For a bit of Calvin&Hobbes vibes, check out Sandra and Woo, a young girl and her pet talking raccoon.

Kind of surprised Saturday Morning Breakfast Cereal hasn't been mentioned yet. Lots of philosophical hilarity, with notes of science, religion, robots, economics, and nerd references.

As far as things that have been mentioned, seconding Perry Bible Fellowship, xkcd, the Oatmeal, and Cyanide and Happiness