On my niece's birthday, I made some chocolate cupcakes. I used this recipe from MennoniteGirlsCanCook. They share a great range of recipes. It's really a treasure, you should check it out!
Btw, you may notice that my frosting is a bit runny, that's because I used a little too much milk. The recipe doesn't specifically say how much, so better use 1 Tbs first and see if you have reached the consistency you'd like before adding more.