Vitamin e cream mixed with water does the trick for me for under eye circles, but then again I'm vegan now so I don't know if it'll work for non-vegans. Instead of commercial soap, I just rub skin gently with a baking soda/water mix (make sure baking soda doesn't get too close to eyes or under eyes), rinse, rub softly witch hazel on skin for prevention and treatment of acne and then put the vitamin e and water on and let dry. I use baking soda and water for my teeth also, but I make sure to lightly brush away from the gum line because the particles are harsh to flesh.
The dark circle could be diet also, I would drink more water for our bodies are 75% water. Rest and exercise is also good. If all else fails it's just genetics....