Music
Music is pretty much an essential element of the human existence.
I enjoy listening to music whenever I can. I also enjoy the freedom that comes with linux to do what I want with my music. In that vein, I'm pretty sure that as soon as I get the chance, I'm going to install RockBox on my iAudio 5 music player. RockBox is firmware for music players. That means it's the brains for your "mp3 player" or "ipod". (Please call it a music/media player. Hopefully whatever media player you own, it supports far more than just the mp3 format; and ipod is just a brand.)
The iAudio is pretty neat the way it comes out of the box, and I bought it specifically because it is one of the brands that support the free ogg file format. But the RockBox software is even cooler. It is completely configurable to do what you want it to do. It will even talk to you so that you can hear the menu instead of squinting at the tiny screen in broad daylight while driving in traffic (not that anybody ever does that).
Well, I was going to but upon more investigation, the RockBox firmware isn't available for the iAudio 5, just the iAudio M5. I'm not a hardware engineer nor a driver developer, so I'm not going to develop that support. I'll just enjoy my Cowon the way it is.