A couple of the ones I really like:
https://www.youtube.com/channel/UCcIbMAd5E6cOaJRuIliW9Lw - This guy was the one who really helped me get a grasp on RC electronics when I was just starting to get serious in the hobby. May he rest in peace.
https://www.youtube.com/channel/UCQ2sg7vS7JkxKwtZuFZzn-g - Who can forget the world's most vocal Kiwi?
https://www.youtube.com/channel/UC7BicwcRMDu3Ed1CJ7BZsxA - Doesn't post a lot but his channel is still cool because a lot of the stuff he builds is just so weird. Like taking 9 airplanes and joining them by the wingtips!
https://www.youtube.com/channel/UCTXOorupCLqqQifs2jbz7rQ - Much heavier on the technical aspects but still well worth watching
https://www.youtube.com/channel/UCCKDHzGUWhVXxdx0sZG7DCw - I think this guy was in a Flite Test episode a while ago
https://www.youtube.com/channel/UCjm3ivk56m794jkGxutejcg - This is technically not an airplane related channel but I still watch it because engines are still very cool
https://www.youtube.com/channel/UC5lXh5HZ62N8s7urLVoOVxg - Builds the most beautiful rubber free flight airplanes I've ever seen.
And I guess I might as well mention my own channel. Technically I run it jointly with a friend and he edits and uploads most of the videos, but the flying footage is about his and mine 50/50 unless stated otherwise.
https://www.youtube.com/channel/UCQb2GzN8hcGyU4UPT0nLFCw