Just a few of my favourites:
Tantacrul - Irish bloke - does great video essays on music theory and technology
Whang - Millennial nostalgia for people who like stories about the early internet (some of them quite grim)
Alex O'Connor - Theologist & Philosopher, tackles the big questions and a brilliant debater, Hitchens-esque
Captain Disillusion - Special FX expert, debunks videos of dubious authenticity in an entertaining way
Defunctland - Does a great docuseries on old theme park attractions
Jim Browning - Like the digital version of batman, takes down scam call centres
Horses - A new channel I just subscribed to, makes video essays on various topics relating to art and history
HardestGeezer- He's trying to run across the length of Africa from SA to Tunisia - that's pretty much all there is to it
GeoWizard - Plays geography related games but most famous for his straight line series where he attempts to walk across entire countries (usually Wales) in the straightest line possible.