I'm a big fan of the Beachbody workout programs. Especially Insanity. I've completed it twice over the last year and a half. Now I use the workout as my regular cardio. P90X is different. It's more strength workouts then cardio. I mix the two programs. I highly recommend taking a multivitamin and eating enough healthy foods with Insanity. Because you sweat so much and burn so many calories you body loses a lot of nutrients. After every workout I usually make a whey protein shake mixed with half water and half milk. It's important that you feed your muscles after these kinds of workouts. Don't worry you're not going to ruin your workout by consuming calories right after. They call it "free calories" Your muscles will absorb the protein and burn those calories and more 10 times faster then if you didn't have a shake. Check this out.
yfrog Photo : http://yfrog.com/6xjhkuj Shared by This is how many calories I burned in an hour with the Max Interval Circuit from round 2.