For chocolate pie filling: Add 2-3 tbs cocoa to the mixture while heating on the stove.
For chocolate peanut butter pie (my all-time favourite): Mix 1/2 cup creamy peanut butter with 1 cup icing sugar until the mixture resembles coarse cornmeal. Place this mixture in the bottom of a baked, cooled 9" pie crust. Pour chocolate pie filling over the peanut butter mixture and cool. Top with whipped cream and flaked chocolate.
Adapted from Ugly Crust Pies