TreeFrog, which Podcasts are your favorites? I already admitted my addiction to "This American Life," so it's your turn now. ;-)
NPR Music - Music, commentary, and interviews excerpted from All Things Considered and other NPR shows. Covers all kinds of music, literally. Recent podcasts have included Mexican buskers who do acoustic Led Zepp covers, a high school choir competition, remembrance of Duke Ellington's birthday, a preview of new spring alt-rock releases, a Macy Gray interview, you get the picture.
NPR All Songs Considered - Podcast only, no broadcast. Younger artists in the less-commericial pop and rock. Good recent shows were Nellie McKay, Modest Mouse, Fountains of Wayne. The antithesis of hip-hop, country, and American Idol.
In the Groove - Jazz from Connecticut public radio. Ken Laster hosts. A different theme each week. Full cuts, unlike many music podcasts worried about copyright issues.
Florida Stories - From WUSF. Interviews from their oral history project. Folks telling about their personal histories in FL. Much more interesting than it sounds.
I can't remember which of these are already in iTunes' list and which I found myself. If you can't find the URLs I'll post them.