Most of the time I just like to wander throughout YouTube and see where it takes me, but I do have some favorite channels I could share.
A couple of really old ones (that are discontinued now) are:
MissHannahMinx - A sexy girl who talked about basic Japanese language, culture, and travel tips. I miss her JWOWs and Comic-con coverage.
Mordeth13 - Basically, a vlog of a biker living as an English teacher in Taiwan. (His original channel was banned and he lost most of his videos.)
More recent favs are:
Screen Junkies - Love the 'Honest Trailers'.
YesFunnyYes - Often good for a laugh.
Machinima - Good source of various entertainment.
Vsauce - Great perspective and explanations regarding various interesting subjects, as mentioned by u9y42.
VICE - Source of unusual mini-documentaries.