One I can remember from the top of my head is "How to ACTUALLY Use Breath Support". Seemed like a good, in-depth explanation of a fundamental topic:

https://www.youtube.com/watch?v=MC1iJfWA1aQ

The channel I've watched the most videos on is Chris Liepe's. The video "STOP Singing Vowels this way! (its making you tense)" was in my singing playlist:

https://www.youtube.com/watch?v=yWimkesJDIc

I would still describe myself as a beginner, so please keep in mind that I can't possibly vouch for the quality or accuracy of any of these videos.