Well, let's start by showing off them ZDer channels (Crimson Cavalier, Vergoagogo, Channel ZD-i, TriforceP, some others I'm forgetting), then moving on to ones I watch a lot:
Mr Sunday Movies, Movie Bob, and Channel Awesome for film stuff
I still watch a few of the Yogscast channels, though mostly I just listen to the podcast at this point
Peter Hollens and Smooth McGroove for music
How it Should Have Ended and Cinema Sins I guess fit in a category together maybe?
Super Carlin Bros, The Game Theorists, Film Theory, and Kmack Time for theory videos
Richalvarez for his Nintendo fanseries
Matthew Santoro for his Top 10s and 50 Amazing Facts series
... I watch too much YouTube