what are some great YouTube channels worth checking out?

Here are a few of my favorites:

Up and Atom — an educational science channel. She gives plain-English explanations of all sorts of science topics, from quantum physics to computer science and even some philosophical puzzles from history.

TierZoo — a comedy/educational channel. In each video, he looks at animals as though they are playable classes in an MMO, explaining their strengths, weaknesses, and place in "the meta". It's comedy because it's video-game-themed, but it's also well-researched and based on real zoology. It's a riot.

Simone Giertz — you've probably seen clips of her shitty robots. She builds things for fun, profit, and just because. Most of her projects have an element of absurdity. Some of them work.