Numberphile is interesting.
GameTheory is my personal favorite.
Crash Course for intellectual content.
Vsauce is nice.
C.G.P Grey is a good one for interesting discussion topics.
Funimation has a lot of anime on their channel.
CollegeHumor is great for the laughs.
Proximity for music.
Khan Academy for more academic tools, they also have a great website.
RoosterTeeth for their funny updates and great high-quality content.
ComputerPhile(made by the same guy who does Numberphile, Brady Haran.)
I could go on.
Actually don't watch youtube too much anymore, maybe 2 hours a week at max(besides the educational channels, those are helpful resources).