I have three to recommend:
1. Filkcast. A relatively new podcast by a friend of mine, diving into the world of "filk" music. As a filk musician myself, I think it's wonderful, and it's introduced me to a lot of new music. If you already know/love filk, it's terrific. If you don't know it but like science fiction/fantasy and folk music, you might find something new to love!
2. Hardcore History. Long-form history studies (4-5 hour episodes, with multi-episode series often stretching over 20 hours). The one-off "Celtic Holocaust", about Ceasar's invasion of Gaul, is a good start to get a feel for how it works. The epic "Blueprint for Armageddon", about WWI, is my favorite (and the most bleak). Very much enjoying the current series, "Supernova in the East" (the rise of Imperial Japan, culminating in WWII).
3. Philosophize This! Hour-ish long episodes of the history of philosophy, each episode centered on a particular philosopher or related school of them (sometimes a few episodes for particularly important figures). Starts with the earliest ancient Greeks, and builds forward to almost the present day (recent episodes have covered recent concepts like semiotics, and thinkers like Jean Baudrillard and Michel Foucault.