Music is a big part of what gets me through the cardio portion of my workouts. But after a while, even my reliable Kylie Minogue can get a little tired — enter Spotify. Not only does the app offer a selection of different playlists by genre (including workout music and my dance workout) it customizes daily playlists based on songs you've previously listened to. Run Hundred is another great resource which spotlights the hottest new music by speed to sync with your next jog or sprint.