Ones I'm on at the moment:
Ricky Gervais XFM podcasts:
Basically Gervais, Steve Merchant and Karl rambling for an hour. It's the funniest thing I've come across, there's 4 seasons of radio and then Guardian podcasts, its absolutely fantastic.
The Anfield Wrap:
Everyone should know about this anyway, but good Liverpool chat.
Kermode and Mayo:
Film reviews every Friday, great interviews, great analysis from the good doctor. Check out Kermode's rants on YouTube too, he mullers some films to a pulp.
Stuff To Blow Your Mind:
How Stuff Works podcast, informative podcasts on all manner of topics from biology to mathematics to history.
Infinite Monkey Cage:
Brian Cox and Robin Ince, science based fun. They're a very good pairing with Brians knowledge and Robin's humour.
Occasionally download Daily Bacon, the radio 5 show by Richard Bacon, guests and chat about the weeks events. His science bit "Bacon's Theory" which I think is on a Monday is decent.
All of those are great, but the Ricky Gervais ones have taken over my entire listening schedule.