Decline Push Ups
Push ups are great for building upper body strength, but if you want to add a bit more difficulty, try it with your feet higher than your hands. You can easily customize the intensity of this exercise simply by adjusting the bench height.
Add some weight to the basic lunge and kick up the intensity. This exercise is a solid whole body workout. By holding weights overhead while performing a lunge, you build strength, power and leg speed, while engaging the core for stability. If this is too hard, hold a set of dumbbells in your hands during movement until you build up.
Lat Row Push Ups
Take a pair of moderately heavy dumbbells, and use this exercise to build your upper body and core. Done properly, this compound exercise uses muscles in the chest, shoulders, arms, back, abs and even the legs.
Medicine Ball Push Ups
Try doing a push up with one hand supported on a medicine ball (or other raised surface). It's a nice core stability exercise, but it also alters the range of motion of a basic push up so you work the muscles in a slightly different way. Pass the ball back and forth between reps and you'll get a complete upper body workout.