Pandora

It's easy to grow tired of listening to the same iTunes songs, day after day. Pandora addresses that problem by supplying a constant stream of free new music to your phone. You start by listing some of your favorite songs and artists. Pandora finds patterns in your preferences and creates customized radio stations. You can designate a channel for classical piano performances, another for upbeat '80s pop and a third for contemporary jazz. Or make one just for workout songs. Last.FM is a similarly useful music discovery app. Both services can incorporate your friends' musical picks too.