Since I work from home a lot, YouTube is my preferred source of background noise. I generally prefer less serious channels: since I do occasionally have to get work done, I'm not generally able to watch anything I have to pay a ton of attention to. I also like background noise for gaming, and these usually do pretty well.
Most everything focuses on gaming and movies, and I'm looking to expand. Some of my favorites:
Funhaus. Associated with Rooster Teeth, it's a gaming channel run by a group. Superb production values, and great dynamics among them.
Qull18. Lone let's player who focuses on strategy games, which is my cup of tea.
BirgirPall. A couple Icelandic guys go out of their way to break games. Excellent editing, and non-stop contagious laughter.
Shammy. Doesn't upload as often as I'd like, but really well-written game reviews.
RedLetterMedia. They of the 3-hour Star Wars reviews, they do current movies and have a great series (Best of the Worst) where they watch terrible B and edutainment movies and talk about them.
Oliver Harper. His current movie discussions aren't that interesting to me, but he also does retrospectives on classic films from the '80s and '90s.
Nerdwriter1. Awesome discussion about creative stuff, whether it's art or (more commonly) film.
Lindsay Ellis. Used to be associated with the Nostalgia Critic, but is thankfully on her own now. Really good pop culture analysis.
CloudCuckooCountry. Book reviews, plus a really fun series where they do live readings of terrible fantasy novels they find on Amazon.