Deep Knee bends - Builds thighs, glutes, hips and great for lung power and endurance. With your feet about shoulder width apart, grab on to the edge of a sink (or something that will give you support) and while looking up slowly bend your knees and lower until your butt is just about touching the floor. Slowly stand up again using only your legs to lift you, keep your heals on the floor and do as many as you can. For variation you can place your feet wider or closer together, or do them one leg at a time.
Calf Raises - Do them on steps, put your toes on the edge of a step and hold on to the hand rail for balance, lower your heals to get a good stretch, then raise up on your toes as high as you can, lower and repeat for as many as you can. For variation try them in the squatted down position, one leg of a time or donkey style.
Chin-ups or Pull-ups - For building back, shoulders, and biceps. Grab a bar with an under hand grip and hang down getting a good stretcth in the lats, Pull up until your chest hits the bars, lower and repeat for as many. These can be easily be done in a park, school yard or on a doorway chin bar. Also try with an overhand grip, with one arm at a time, or even on monkey bars using a parallel grip (palms facing each other).
Push-ups - For building chest, shoulders and triceps. Lie face down on the floor hands about shoulder width apart keep your palms turned inward slightly, push-up until your arms are straight, lower and repeat for reps. To make it more difficult elevate your feet. Also, try different hand placements (closer together or farther apart). They can also be done between chairs, this was the favorite exercise of Charles Atlas. Another variation is Dips between parallel bars.
Handstand push-ups - Great for shoulders and arms. Get into a handstand next to a wall, put your toes against the wall for balance, lower yourself until the top of your head touches the ground, push back up and repeat for many reps. Try both close and wide hand Placements.
Crunches - For firming abdominal and reducing stomach. Lie on your back with your legs bent and your heals close to your butt, put your chin on your chest and your hands behind your head. Raise your head up crunching your abs hard (you should only go about 1/3 of the way as compared to traditional sit-ups) lower and repeat for lots of reps.
Hyper -Extentions - For strengthening your lower back. Place a chair near a bed, while lying face down with your hips on the chair and your lower legs shoved between the mattress and box spring, put your hands behind your head and bend forward at the waist as far as you can, raise back up until your back is straight and repeat for reps.
Grip Exercise - To build forearms and hand strength. Use a store bought pocket hand gripper, or a hard rubber ball that fits in your hand, squeeze as hard as you can, relax and repeat for many reps. Also try just the thumb and one finger at a time, exercise each finger this way.