This American Life is my favorite radio program. It finds real people doing interesting things and tells their story in a compelling way within the confines of a one hour weekly broadcast. The producers build the story against a compelling infusion of music always perfectly suited for the events unfolding throughout the course of the hour and there's always a sense of identity that makes you care about the story being told, even if the point of view isn't something you identify with.
Or in the words of the show's creators, "It's a weekly show. It's an hour. Its mission is to document everyday life in this country. We sometimes think of it as a documentary show for people who normally hate documentaries. A public radio show for people who don't necessarily care for public radio."
I almost never remember to tune in when the show airs, because the timing doesn't fit my schedule. Having the option to subscribe is perfect, because it supports the show and I get it on demand.
The iPhone and iPad app are both an outstanding extension of the show. You get access to all the episodes, dating clear back to 1995. Archives can be streamed for free or you can pay for individual episodes. You also get a ton of behind the scenes content, including outtakes and radio shows produced by Ira Glass before he started doing This American Life.
The only thing that would make the app more appealing would be for them to include the comic book about how to make a radio show, which would look amazing on the iPad.