I like the ability to change songs, playlists, etc. on the fly. 1,000 songs to choose from.

 

I just bought an Ipod Shuffle (2GB). It is so small and light I just clip it on a cable on the bars. Works perfect and holds a lot of music. The battery on it last 12 hours (I know because on my way back from Yellowstone we rode 12 hours and it died right before pulling into the hotel!