Discovery and History Channel
It's hard to find interesting documentaries or shows playing on the Discovery and History channels (and similar channels) other than in the early mornings. Rather than informative shows about history, animals, technology, and other academic subjects, they show reality television. This would include shows about fishing in dangerous conditions, gold mining, and living in the arctics. Thankfully, I read somewhere that the number of reality shows has been on the down-slope. Maybe we'll return to the good ole days of documentaries all the time.
Personally, I really enjoy good historical and/or informative documentaries (at any time really). And I would never subscribe to cable for that purpose since majority of those channels play reality television constantly; it's an obsolete turn off. It would be nice to just turn on the television and watch something random and learn about it though. But the best alternative seems to be searching through Netflix or other streaming services. I really they had a randomize feature though; sometimes it's just easier to just have something play automatically and you just tune in.
Some enjoyable documentaries I've seen recently: WWII From Space and The Search for General Tso. For sports fans, the 30 for 30 series are almost always fascinating.