You can use some of the following directories to locate podcasts:

Odeo
PodNova
Podfeed
Podcast Pickle
Podcasting News
Podcast Alley
Vital Podcasts
Digital Podcasts
Pod Blaze
Idiotvox
Pod0matic

To locate videocasts or video podcasting, you can use the following directories
Video Podcasting section of Podcasting News
Vlogdir
Podcastvideos
Vodstock
MeFeedia

Advertisements