So, these are the podcasts I'm currently subscribed to, in no particular order. I'll give them a little mini-review each.
The Bungie Studios Podcast - mostly shilling for Halo stuff, highly irregular, but still amusing.
Writing Excuses - professional writers giving their advice on how to write professionally - everything from "how to avoid being formulaic, even when following a formula" and "what editors do and why you need one" to "how to submit your work for publication". Bite-sized fifteen-minute chunks of advice, from people who have done what they're telling you about, and have good chemistry.
Fear the Boot - this was the first podcast I listened to, and it pretty much spoiled me for other podcasts. Production quality and host chemistry is excellent, and the RPG advice is well-considered. This was also the only podcast I ever listened to from a portable mp3 player (episode 82 dropped the day before I came to the US).
The Podge Cast - after some host drama which I won't go into here, ex-hosts of Fear the Boot created this podcast. They're still insightful, and the quality is still good. They range wider than RPGs, but they remain mostly focused on such things.
Bear Swarm! - A cross between Fear the Boot and the Podge Cast, with a little more swearing. Good fun, and mostly good advice.
Atomic Array - another RPG-focused podcast. Still under review, but pretty good so far.
Game On! With Cody and John - this one's about board games, and is nicely entertaining.
Save Against Frostbite - slowly improving sound quality (they've finally killed the hum, and hopefully soon they'll manage to figure out turning the gain down to stop the mics clipping) and huge amounts of profanity, from a bunch of Canadian geeks talking about anything and everything.
I also have Radio RTFM and the Red Earth Saga in the list, but those two both appear to have suffered what's known as podfade.