Becoming Bond was a very fun documentary on how and why George Lazenby starred as James Bond for only 1 film. It's almost an autobiography, since George pretty much narrates the entire thing. I think it's an interesting enough story for anyone, but definitely a must-watch if you're a Bond fan. This is a Hulu exclusive.
History of the Eagles is a very well-made documentary of the band The Eagles (and if Luke was here he would say what he always says when I bring up the Eagles). As far as band documentaries go, this is the best one I've ever seen. Just the way it's edited, it's very entertaining to watch. Most other band documentaries I've seen where very boring to watch. This documentary makes me want to sell all of my possessions, with the exceptions of my musical stuff, move to California and try to "make it" in a rock band. This was on NetFlix, but I don't know if it still is.
Room 237 is a documentary about the movie The Shining. Stanley Kubrick's films are.. well, they're Kubrick films. You can pick them apart and come up with a million different meanings for things. Room 237 explores many theories of what exactly is going on in the movie The Shining. I find this documentary very fun to watch. There's something about it, maybe just the way it's edited, that makes it feel like you're really uncovering hidden meanings within the movie. I've seen this come and go on various streaming services, not sure where it's available now.
The Men Who Built America was a miniseries that aired on The History Channel. Vaderbilt, Rockefeller, Carnegie, JP Morgan, Edison, Henry Ford. These people all died ~100 years ago, and they are still household names. This documentary explains why. I don't know how historically accurate it is, but it was pretty entertaining.
These next ones aren't so much documentaries, but along those lines.
Dark Matters: Twisted But True is a series I use to watch back when I had cable. Each episode is a couple of short (true) stories, and the stories are all something slightly or completely horrific. Narrated by John Noble (Walter Bishop from Fringe) with recreations for each story.
Select episodes of
How It's Made stream on Hulu or NetFlix, and I think you can even catch some of them on YouTube. I've always enjoyed watching this one.
If you like Technology connections, LGR, et cetera (those are all great channels!) then you may also like
The Computer Chronicles. This is a TV show that aired from 1983 to 2002, and a lot of the episodes are on YouTube.
https://www.youtube.com/user/ComputerChroniclesYT/about