there are ways of changing the stimulus for pushups. I often do things like putting my toes on a swiss ball. Also, try having one arm raised up a bit higher in a platform, for stabalizaiton training I like putting one hand up on a wobble board or you can put one hand up on a medicine ball. Then to get reall creative have one hand up on a medecine ball and do a push up, as you are coming up roll the ball to your other hand, catch it and begin another push up rolling the ball back and forth. Once that gets to easy try elevating your feet on a bench and then a swiis ball. You can also try ballistic type of pushup. Go into an aerobics studio or somewhere that you have a lot of room and take a medecine ball. Place both hands on the ball and do a push up. As you come off the ground thrust your body up into the air and rotate as far as you can in one direction. Keep going until you complete a full 360 degrees. Do that a couple of times, that is really tough.