Over the past few years, podcasts have become as ubiquitous as TV, movies, and books. They're hands-free, portable, unobtrusive — i.e., perfect for commutes — and usually free. Oh, and the content itself is as wide-ranging as it is enjoyable. There's a podcast for everything. Want to learn about an obscure bit of history? Hear really smart people's thoughts on politics or pop culture? Creep yourself out with true-crime stories? Laugh hysterically to yourself on a quiet subway car? Yeah, there's a podcast for all of those things — and more.