Insanity, in my opinion, is one of the most, if not THE most, incredible body conditioning programs out there.  It is definitely an advanced program and only suitable for people who are already in decent shape.  When I call it a "conditioning" program, that means it will help you burn fat, increase your speed, power, and overall athleticism, will work wonders on your legs, and will tone your core.  It is not a weight training or upper body-focused workout.  However, the program requires no equipment, except an optional yoga mat for one of the DVD's.  You are using your own body as resistance throughout the entire program.  Insanity is basically 6 days a week of intense plyometric cardio - lots of running in place, jumping jacks, squats, jumps, push-ups, and floor drills.  Most of the DVD's are set-up in an interval circuit format, which I discuss a little bit more below.  Made up of 10 DVD's, Insanity is a two-month program.  The first 4 weeks include DVD's between about 30-40 minutes in length, while month 2 includes workouts up to 60 minutes in length.  Insanity also comes with an excellent nutrition plan, and there is a possibility to expand to the "Deluxe" edition which includes 3 advanced bonus DVD's.