Audio based resources
EdTechTalk
All of the EdTechTalk webcasts are posted as downloadable podcasts after they air - anywhere from several hours to several days (sometimes weeks) later, depending on the host. You can either listen right from the webpage, or download the mp3 file, which can be played on your laptop or put on your mp3 player of choice.

EdTechTalk Podcasts Tour from Sarah Sutter on Vimeo.
iTunes
iTunes is a great tool for accessing podcasts of various topics. Podcasts and Vodcasts (video) are available for free through the iTunes Store. It takes a little searching to find the ones that are right for you, but chances are there are several podcasts that will appeal in terms of topics, duration, and style. My favorites are BitByBit Seedlings, EdTechTalk, David Warlick, Wicked Decent Learning, and the occasional Tech Chicks or EdTechPosse.
iTunes Podcast Tour (screencast)

iTunesPodcastTour Part 1 from Sarah Sutter on Vimeo.
K12Online
The K12Online resource is an annual posting of professional development podcasts and vodcasts. Most are available in both audio and video modes. Some work best in video as the presenter is using screencasts to demonstrate an idea, but some are mainly discussion or idea based and can be very effective in just the audio mode. Each year new topics are posted in October, but the past years work is archived for you to experience at any time. This year (October 2008) there were two strands, getting started and kicking it up a notch. If you are a beginner, you may want to start with the getting started strand.
K12 Online (audio AND video options)

K12Online Tour from Sarah Sutter on Vimeo.