When most people use the term cardio training, they refer to running on the treadmill, spin classes, or using the cross trainer. What most people don't realize is that these can be ineffective cardio training tools at times, as your body develops resistance to exercise quite rapidly, and your body demands change and further exhaustion to get results.
So if you routinely use the same cardio equipment, change it up. Not only can you change your cardio routine by changing equipment, but you can change it by NOT using equipment and use your body weight!
Star Jumps/Jumping Jacks are a GREAT cardio work out that DO NOT require you to use fancy equipment. Building your endurance on these will tone you up fast!
Jump Rope (only a rope) will improve your agility and will help get your heart rate up!