Counter-Top Push Ups

This is one of my favorite exercises...I struggle with the traditional floor push-ups, and this one seems to be just as effective.
As the name of the exercise states, you can do these by leaning with your hands on a counter-top (I actually stand in front of the kitchen sink).
Place your hands about shoulder width apart on the counter with your elbows facing outward. (Your fingers will be facing each other).  Stand far enough away from the counter that your arms are straight, you will be 'leaning' on the counter-top.  Place your feet about hip width apart.  Inhale, contract abdominal muscles and lean toward the counter-top, just as if you were doing a push up from the floor.  Lean far enough that your elbows push out to a 90 degree angle.  Exhale and push yourself back.  I repeat these about 15 times and do two sets.  By having your elbows facing out, you will really feel the pull in your muscles across the top of your chest.  You can also perform push ups similar to this using a Smith Machine.