Here is an extremely effective but advanced exercise for strengthening the feet and lower leg, and will help you master the ever important tripod foot. This exercise is also anti-rotational in nature and will help you strengthen your core. Last but not least, this exercise will strengthen the muscles in your chest and shoulders, especially if you add more weight to the bar. However, the main goal of this exercise is to strengthen your feet, so check your ego at the door and don't sacrifice form for weight.
To perform this exercise:
Stand on one foot, and have a slight bend in your knee. Make sure that the weight is on the mid/back of your foot, and that all of your toes are in contact with the floor, particularly your big and baby toe. This is a tripod foot base. Grab onto the barbell and perform a fly. Once you have performed the desired number of reps, switch feet.
The key to this exercise is to maintain the tripod foot the entire time, and to maintain full body alignment. Your knee should not collapse in or fall out, your pelvis and torso should remain totally level, and there should be no rotation occurring in your body whatsoever. I won't lie, this exercise is significantly tougher than it looks!
If you want to learn more about foot strengthening, here is another article I wrote a while back.