---begin rant---
I'm a little worried by the fact that people get bored riding their bikes solo. If cycling is a hobby, you need a new hobby. If it's a social thing, always ride with friends or make up your own friends or make calls with a bluetooth headset. If you cycle to get in shape, HTFU. I sit in classes everyday and wonder about the state of my peers when they can't keep their cell phone in their pocket for 50 min.
---end rant---

Nature, my own thoughts, and podcasts have always done it for me, in that order.

Add 'Stuff You Should Know' to the growing list of recommended podcasts.