Also consider subscribing to:

TheRoyalInstitution (science stuff, professionally done)

periodicvideos (excellent channel, chemistry stuff)

numberphile (math)

minutephysics (physics)

sixtysymbols (physics/math stuff)

DeepSkyVideos (space stuff, not updated often)

psyfile (psychology, not updated often)

engineerguyvideo (was really good, now rarely updates)

computerphile (brand new channel, no content yet, from same guys as the other *phile channels)

and for fun: JoergSprave (the slingshot guy, but his creations are quite cool if you like physics)