Push up variations - all requiring feet in the stirrups:
Put one hand on a medicine ball, other hand on the floor, do a push up. Roll the ball and switch hands, do another push up.
Walk backward on your hands until your feet are up above your head. Do ten push ups, walk forward on your hands.
Put your hands in the middle of the flat side of a Bosu ball, pull knees in to chest and then extend back out. When extended, do a push up.
Veronica