Not exactly tech/programming channels, but really good brain snack food...

https://www.youtube.com/user/Vsauce --- IMHO the best youtube channel in existence. Every video is a rabbit hole of interesting questions and tangents with fantastic presentation and weirdly uplifting closing points.

https://www.youtube.com/user/pbsideachannel --- Smart thought provoking videos that use internet memes, gaming, anime, and such as the launch off points.

https://www.youtube.com/user/1veritasium --- Well presented science videos with a focus on the joy of learning.