Apple Ipod (2001)

Portable MP3 players had been around for many years before Apple launched its version in 2001, but the iPod – together with Apple's iTunes software – was the technology that really transformed the way people listened to music. The device's large internal storage capacity meant it was no longer necessary to carry around CDs or cassette tapes, and the sleek design made it a desirable item to own.

Source: http://www.telegraph.co.uk/technology/picture-galleries/11298840/Most-important-inventions-of-the-21st-Century-in-pictures.html