It is unfortunate that this "AskHN" turned into a link dump. This could have been a much more interesting discussion if people capped their list of favorites at two or three channels.
Bookmarked!
I often use youtube as my primary search engine, and that's working well. While the recommended videos (without searching) on the front page are often relevant, I've not had a very rewarding browsing experience. All these links strike me as a way to bootstrap a better browse.