Photos: iPod through the years

The iPod U2 (20GB only) shares most of its characteristics with the fourth-generation iPod but boasts a few key differences. The most noticeable is the player's black body and Ferrari-red scrollwheel--it definitely pops. Flip over the device, and you'll find another distinguishing design tweak: the signatures of all four U2 band members have been laser-etched in the iPod's shiny, silver rear casing, which also features a U2 stamp and the words "special edition."