Digital Rev are certainly one of the better ones out there, and they are the largest of any.... Feel that Tony Northrupp should have been included, even if he is a little out there sometimes. Matt Granger posts some great reviews and tutorials.
My Personal Favorite is Jared Polin, though I am sure he is hard to take for many viewers.
Its looking like a great source to learn for the Photographers. Thank you for the thread.
I'd add B&H. Maybe it's advertising and so can't be mentioned, but their presentation videos where they get an expert in and film the lecture are just great - obviously one picks and chooses subject matter, and sometimes the presenters are better than others. But what a resource!
It will be interesting to see what happens to Digital Rev with the loss of both Kai, and Lok last month. Both of which have started their own channels subsequently, expecting big things from Kai, he has hit over 200k subscribers already.
Great source to learn about photography. Thanks.