Ohhh, this can be fun...
Let me see, as for upper-body, there are all sorts of push-ups.
Regular push-ups, which are pretty self-explanatory.
Elevated push-ups, put your feet on a chair.
Vertical push-ups, put your feet against a wall and your hands no more than two feet away from the base of that wall.
Deep push-ups, use three chairs, one to support your feet, and one for each hand... When going down, go past where the ground should be.
Superman push-ups, start with your butt in the air, arch down so that your chest brushes the ground between your hands, then continue forward so that your head is up, but your hips are almost touching the ground... then reverse the motion to complete one repetition.
Wide arm push-ups, just like regular, except that your arms are further out.
Close hand push-ups, same, except closer. Usually at least the thumbs touch.
Diamonds, your thumbs and forefingers touch.
Diamonds you can afford (on a soldier's budget, at least, since that's where I heard of these), thumbs and fingers completely overlapping, so that you can't fit a one ct. diamond between them.
Four man push-ups, get three adventurous, foolhardy jocks and have them lay down, face down, to form a square, so that the feet of each person is on the shoulders (!!not neck or middle back!!) of another person... then, carefully timed, everyone does a push up at the same time. This effectively doubles the weight of a regular push-up, though it depends more on the coordination of your buddies as to whether you can do one successfully or not. Any attempts to do thise close handed will almost certainly fail.
Clapping push-ups. When going up, push with enough force to propell your upper body off the ground, and while momentum is still supporting you, clap once. Great for showing off.
Any of these, except the diamonds and clapping push-ups, can be done with closed fists, which helps to develop the lower arms more, but your knuckles will be hurting until you get used to it.
Non-push-up, upper body:
Overhead arm clap: Start with your arms horizontal, palms up, and simply clap above your head. With each repetition, work on keeping your arms as straight as possible (someone with a big head like mine is allowed to bend their arms at the last moment so that they can actually clap
), and keep the arms as close to horizontal as possible when you're starting each new repetition.
Not sure of the name: Simply hold your arms out horizontally for as long as you can. It burns. For showing off, grab some heavy hammers and hold those out while a friend times you... then try to get him to match your time.
Cherry pickers: Arms horizontal, simply open and close your hands. It burns faster.
Small circles: Arms horizontal, circle your arms, either backwards or forwards, keeping the circle no more than a foot in diameter. It relieves the burn of cherry pickers, but quickly adds its own burn.
Abs:
Sit-ups: Make certain that you have good padding.
Crunches: Most people don't do these effectively. Hold your muscles tight for at least three seconds per rep.
Flutter kicks: I absolutely loathe these. Laying flat on your back, raise your feet about 6 inches off the ground, then raise one foot while lowering the other... alternate... keep going until you can't stand the burn, then push yourself even farther. Don't go too fast, because exercising is for your bennefit, remember?
Most of the other abdominal (abominable?) exercises are much easier to show than explain... If you want a good ab workout, try doing sit-ups on a slope with your head downhill.