I've found that decent programming podcasts are few and far between. The ones that promise to be most useful - as in, actually teaching you how to do X - suffer from the flaw that they are people talking about code. And, obviously, if you are driving or running or whatever it is you are doing such that you are listening to audio podcasts, you can't see the code. If they get into any level of detail, it all falls down.
Imagine: "well, the code is like this - open brackets defn whatever open brackets map open brackets list open brackets whatever clsoed bracket closed bracket" (for Lisp) or "well, we created a class with a method called foo that iterates through the 'bar' argument, and returns a array of strings" (for Python/Java etc.)
I tried listening to a podcast like that (about Python IIRC) when I was on the Eurostar train once. I did have my computer with me, but I just couldn't follow it without being able to see the code. At the point I realised this, I was deep under the English Channel, so couldn't exactly log on to the blog and see the code samples...
The closest things I've found are either things like RailsEnvy - now reborn as The Ruby Show and not IMHO as good - which provided some useful news each week about new libraries and plugins for Rails. Or there's some higher level best practices, software engineering type programmes which often seem to be people preaching to me about how I need to be more and more test-infected and agile and (insert methodology buzzword of the week).
It's actually quite difficult to find good, geeky/programming-related podcasts that don't either just descend into general news chit-chat or end up with someone trying to sell me a new engineering methodology. It's a very hard balance between being too technical for audio-only and not being technical enough. A lot of the newsy podcasts like TWiT are way too damn long and rambly.
I mostly don't bother with tech podcasts for the reasons I've just described and stick to things like In Our Time, and quite a few course podcasts on philosophy and other interesting stuff - quite a lot of universities are now doing podcasts: Oxford, UC Berkeley, MIT, Stanford etc. There are thousands of people now following along with lecture courses remotely using podcasts - see http://www.latimes.com/business/la-fi-podclass24nov24,0,7889...