Mostly history nerd stuff and HEMA channels, like Lindybeige, Schola Gladiatoria, and Max Miller. My current favorite is probably Jackson Crawford (professor of Old Norse studies, does lots of videos on vikings), but Lindy is the all-time great.
I've kept up with RLM ever since the Plinkett days, and I used to follow their gaming channel until it got discontinued.
There's a variety of Bullshido and weeb channels I like to have on in the background, also some STEM stuff, although a lot of that doesn't work as well as background noise. Something like Practical Engineering or Periodic Videos is fine as background noise, but anything as complicated as, or more complicated than, NileRed really demands my full attention (3Blue1Brown, for example)
Various lectures, if I can find them. Some require attention, but others are fine as background noise.
Audio books are always fun, although most of them have been purged by Google, so that's a shame.
A bunch of obscure philosophy and political channels; my favorite has long been James Corbett, but I find I mostly agree with him, which is not very interesting. So I try to make myself branch out, to everything from weird commie stuff, to Varg and Edward Dutton. Molyneux before he got purged, but his jannies kept banning me for disagreeing with him.
Speaking of commie stuff, there are several New Age channels I flip on from time to time; Teal Swan and Sarah Landry, mostly. Again, I like to balance the New Age dingbat vids with, for example, Christian channels, pagan channels, and old Meir Kahane clips.
And speaking of Teal and Landry: lolcow channels. There's several lolcows I regularly have on in the background. Too many to list right now; I'd have to dig through bookmarks and playlists.
Monitoring this thread. I'm the same way. Always looking for new stuff.
Most of the stuff I listen to is either politics, old Howard Stern clips, or wrestling shoot interviews. Lately I've been hooked on this true crime podcast "this is MONSTERS". Really good stuff with new episodes weekly.
If you're looking for straight up podcasts, anything by Lindsay A. Graham is good if you're interested in history. "American Scandal" is really great, especially the series on the Hare Krishnas. "American History Tellers" is pretty decent too, but it has a little bit of a left bent. Not as pozzed as 99.9% of the stuff out there, but you still pick up on it.
If you like wrestling, you might enjoy
OSW Review; they're Irish smarks who've been doing retro commentary for almost a decade now.