I received a gift of an MP3 player and have been listening to podcasts while I exercise.
The first and best is Buffy Cast about Buffy the Vampire Slayer. There are only 13 episodes and two speakers. The presentations are thoughtful and cover topics such as Xander’s character arc the episode, “The Body.” There are several I want to listen to again. (defunct 2011)
Stars Hollow – husband and wife podcast on Gilmore Girls. I haven’t seen the episodes they discuss but they are lively and sweet and I enjoy it anyway.
Movies You Should See – a group of reviewers from the U.K. who analyze various movies new and old. I enjoy the group’s easy banter. Although they are kinder to some movies than they should be, they seldom suffer dullards and fakes. (still active 2011)
Another one on Buffy the Vampire Slayer – Buff Cast. Each Season is covered by one or two podcasts. Some of them are long, about three hours. Sometimes they devolve into recaps but they include interesting trivia. (defunct 2011)
There are others but I haven’t listened to enough to know whether I recommend them or not.