The digital MP3 player, instantly recognizable by its white earbuds, has become hugely successful over the past four years for the way it's revolutionized the way we listen to music.

There's something very hip about holding an iPod. Not only is the device very visually appealing, but it gives the user access to hundreds of songs in something no bigger than a human hand.

There are a lot of other imitators out there, but none have been able to crack iPod's stranglehold on the market.

So if it seems that everyone has an iPod these days, it's because a lot of people do.

U2, the band that also acts as a social conscience around the world, has formed an unusual relationship with iPod's maker, Apple, lending its likeness and a song to the product.

U.S. President George W. Bush has owned one since July, a present from his twin daughters. Bush likes to use it when he's mountain biking and his personal playlist includes artists such as Warren Zevon, John Fogerty and country greats George Jones and Alan Jackson.

The iPod, or any MP3 player, is a perfect accessory for athletes, keeping them company during their long cardio exercises or helping them maintain focus before a big event.

With that in mind, we surveyed athletes from a wide variety sports for answers to the question, "What's on your iPod?"

Click here for a photo gallery and their answers.