Besides reading, one of my favorite activities on the subway commute is listening to podcasts, especially the weekend public radio programs OnTheMedia and Studio360. And the latter has had some really excellent shows in recent weeks, looking at the cultural legacy of "American Icons" -- such as Moby-Dick and The Wizard of Oz. Neither of these stories was among my favorites before I heard each hour-long show, but now I have a better appreciation for them. I'm also excited about an upcoming one on Aaron Copland's Appalachian Spring, which is one of my favorites.
Strongly recommended, especially if you have an MP3 player and a 50-minute ride somewhere. (They're also available via iTunes.)