I develop various playlists on my ipod. One day its 70s funk and disco, another its heavy metal, hip hop/rap, classic rock, 60s psychedelic, etc. Sometimes I just do random songs from my entire ipod library (3500+ songs). You never know what's coming and you might have to hit the next button several times, but it keeps it interesting. Music is a great motivator. I look forward to the music...the exercise is just what I do while I listen to it.