I don't know if it's been mentioned here, but my brother just turned me on to
You Must Remember This: "The secret and/or forgotten histories of Hollywood's first century."
I've JUST started listening to it, and so far it's not quite NPR production quality, but the subject matter is exactly the kind of stuff I can't get enough of. The Gilbert Gottfried show is still the closest to my ideal podcast for its balance of entertainment history with humor, but You Must Remember This is so far showing real golden era Hollywood deep-diving promise.
Also, I just have to mention what is probably the worst podcast I've ever heard. It's so bad I'm fascinated with it to the point that I wonder if it is actually some kind of long-con prank. It's called "True Murder: The Most Shocking Killers in True Crime History and the Authors that Have Written About Them" and it's hosted by this Dan Zupansky character who has seemingly no presence on the internet except for this podcast. The show is a long-form interview with various true crime authors, and generally runs from 1-2 hours.
But I'm not exaggerating here: The show literally sounds like it was produced by placing a cassette recorder near the speaker of an AM radio. The quality is so poor that half the reviews on iTunes are from people who couldn't stand to listen to more than a few minutes of it. But audio quality is only half of the problem: The host, Dan, is laughably inept. He stumbles when reading introductions, he asks dumb questions, and he tries way too hard to lead his guests down some predetermined interview path rather than letting the conversation flow naturally. These are things you'd expect a rookie to do, but this guy's done like 230 of these things, and it's still just as bad in every way. It's unlistenable in nearly every way, but it feels like it could be so bad its intentional? But to what end?