I'll go out on a limb here and say that you have heard of the iPod. I think I'll go a bit further and say that you have seen and used an iPod. But have you ever heard of the Archos 604 Wi-Fi? What about the iRiver S10?
Creative Zen V Plus
Sandisk Sansa Connect
Both these fine players do what the iPod does and then some. But chances are you have never heard of them because Apple controls such a significant share of the digital player market. Go to the park and look around at the people who are listening to music. The vast majority of those people will have white ear buds hanging from their ears while their thumb gently glides over a scroll wheel in search of the next song. Coincidence? I think not.
The digital music player market is flooded with alternative players that companies promise will be the next big thing. Many of these players are downright awful. But amidst the bad, the good shine through. And believe it or not, some of these players are actually better than the iPods that they are competing against.