GNU/Linux podcasts are usually available in both mp3 format and in the patent-free, non-proprietary ogg vorbis format.
Linux Action Show – From Jupiter Broadcasting, home of the premiere podcast dedicated to all things Linux
Linux Unplugged – From Jupiter Broadcasting, a spin-off of the Linux Action Show
How to Linux – From Jupiter Broadcasting, a podcast targeted at Linux beginners. At the time I posted this, this podcast is on a hiatus pending a restart expected later in 2015.
Linux Voice – This podcast is produced by the editors of the UK based magazine “Linux Voice”.
Linux in the Hamshack – This podcast focuses on the use of GNU/Linux and free software in the ham radio shack.
Linux at Work – This is a new podcast that focuses on the use of GNU/Linux and free software in the workplace.
Hacker Public Radio – This is a podcast that focuses on “hacking” in the broad Richard Stallman “playful cleverness” sense of the term. While not every podcast is about GNU/Linux and free software, the overwhelming majority of them are.
Bad Voltage – This is a podcast produced by a group of long time figures in the free and open source software community. Not only do they talk about technology and free/open source software, but they also talk about music, culture, and engage in social commentary. Often entertaining!
Linux Luddites – This is a UK based podcast by the “grumpy old men” of the free/open source software community
Mintcast – This podcast is produced by members of the “Linux Mint” community.
You can find an excellent listing of GNU/Linux and tech related podcasts at The Linux Link