Great thread! I listen to mostly L.A. and San Diego sports podcasts. There are a few that are "Must Listen" as soon as they're available and they are:
Pencils Down - Pumpy's Podcast!
Freakonomics - Among some of the podcasts: "What's the Best Exercise", "Should Tipping Be Banned", "There's No Such Thing As A Free Appetizer", and lots more. You'll learn a thing or 2.
60 Minutes - CBS's Award Winning Show
ESPN Olbermann - Sports and sarcasm
Star Talk Radio - My favorite. Where pop culture and science colide. Knowledge and comedy.
48 Hours - Crime
Frontline - Documentaries. One of my favorite show was concussions in the NFL.
Stuff You Should Know - Learn stuff