Cadence.FM (free) is an excellent iPhone app that compliments your workouts by providing you with a constant streamof music that consistently matches a chosen tempo — it’s your “on-demand personal DJ.”
Its best feature is that all of the music it plays is streamed from the SoundCloud music community and includes the best popular remixes, trance, house, dub-step and club music — so you don’t even need to store tracks locally on your device to use it. Just choose a channel and specify the BPM to which you’d like to work out and Cadence.FM will select the music for you — and it does a great job of it!