great freeware available at http://www.mixmeister.com/download_freestuff.html
plug in all your mp3s and put the ones in 88-90bpm range in a new playlist
load the playlist on your playah and go run
not only can you work on cadence to the beat of the music, you also get a cool eclectic mix. for example, my new 90bpm mix includes audioslave, lauryn hill, wyclef jean, the cult, snoop, etc.
best music for the 88-90bpm range is hiphop/rap.