Slowing iPod sales growth has been one of the chief concerns among Apple Inc. (AAPL) investors because the iPod has historically been a major contributor to Apple’s overall revenue growth. The concern stems from the belief that the PMP market is becoming saturated.

More than 160 million iPods have been sold, making it perhaps the hottest gadget of the 21st century to date. But iPods aren't the only player in town.