There is nothing more painful than doing cardio when it is dull, drab and boring. When you go through the motions, feeling like a gerbil on a machine, it just sucks the life and energy out of you. This can also be a huge problem in maintaining that x-factor motivation.
Music is a great investment. Any kind of MP3 player (or CD player, for that matter) with the music of your choice can make a big difference in the level of intensity, the ease of performance and give you the "cardio rush". Corporate Gyms tend to pump the latest Pop album into your brain until you go crazy. This music will not have the same effect as the music that you really like. The music that moves you.
To keep your cardio interval training interesting, just keep your pace with the beat of each song. You'll notice that some songs will get your Target Heart Rate way up there, where you're training at 80-85% intensity. Surprisingly enough, it won't feel like you're going to keel over. The music keeps you moving and you know about how long you'll continue pumping to the pace. Typically the next song is at a slower pace, offering you a little recovery time and an opportunity for your Target Heart Rate to drop before you work back up to the higher intensity again.
Going back and forth, up and down in intensity with music is a great way to keep interval training interesting and fun. You truly will be moved to the "cardio rush" with adrenaline pumping through your veins and making it that much easier to get to your goal.