iTunes itself has a good selection of radio stations. You can also subscribe to audio and video podcasts (MP3 audio files delivered to iTunes on a regular basis - can be synced with iPods). Check out the following podcasts: Coverville, Ask A Ninja, French Maid TV, Tiki Bar TV. If you're into tech news, there's This Week in Tech, CNET Buzz Out Loud, and Diggnation.