Have I mentioned lately how much I love intervals? They are a fast, effective way to increase your calorie output and burn more fat throughout your day. Plus, I just love the feeling of running really fast, maybe it's that bit of fear that I'm going to fall of the treadmill. I definitel live on the edge!
Include intervals at least twice a week to see improvements in weight loss and speed. You can use intervals in just about any cardio workout - running, walking, swimming, biking, stairclimber, etc. Simply warmup for 5-10 minutes then do 5-7 intervals - 30-90 seconds of high intensity (can be incline, speed, or resistance) followed by 90-180 seconds of active recovery (keep moving and catch your breath before you go again). Then cooldown and your done.
3 Fat Chicks had some great treadmill interval workouts. Check it out here.