Workouts using your own body weight are my absolute favorite. You can perform them just about anywhere and they tend to target the entire body.
Mountain Climbers are no exception. They make a great warmup exercise to get your body moving and your heart pumping. Try incorporating them into your next workout!
In a full pushup position (or with your elbows on the ground and palms down if you aren’t quite strong enough to hold your self up yet), take one knee and pull it into your chest so that you are balancing on your hands and one foot. Quickly switch the position of your legs by straightening your first leg and driving the opposite leg into your chest. You should always have one foot off the ground during this exercise. Try to go for 30 seconds and work your way up to 2 minute intervals.
To intensify this move, try using a pair of valslides http://www.valslide.com/ (or furniture slides for a cheaper alternative) under your feet and quickly slide your leg up to the point that your knee meets your chest. Change the position by straightening your first leg and sliding the opposite knee into your chest.
Give it a shot!