Behind The Bastards: An irreverent look at the worst people in history. Not just the obligatory Hitlers, Stalins, and Husseins. Also lesser known bastards like King Leopold, as well as folk who have led to some rather nasty fixtures in modern society (like Phyllis Schafly, Savitri Devi, and Gabriele D'Annunzio)
Dipped In Tone: A guitar podcast
Feminist Frequency: A feminist critique of pop culture and mainstream film and TV
Philosophize This: Overview of various schools of thought in philosophy
Noble Blood: A Mahnke-produced series on some of the most notorious murders in royal history
History of Rome/History of Byzantium: Self-explanatory. Both in-depth with hundreds of episodes.
BBC In Our Time: Documentary podcast series with a roundtable discussion on a variety of topics ranging from history, science, mathematics, and the arts. I also use this to fall asleep (I'm not kidding).
These are just the ongoing podcasts. Pod miniseries I would recommend are "Sleepwalkers", about developments in AI; "Bagman", Rachel Maddow's series on Spiro Agnew; "It Could Happen Here", a speculative look at the possibility of civil war in America (a real upper);