Place all ingredients in a large bowl, and mix with a wooden spoon or mixer at medium speed, until smooth and fluffy.
Variation: You can add 2 tablespoons of un-salted peanut butter to get a peanut butter flavor frosting.

1 16-oz package confectioners, or powdered sugar
6 tablespoons margarine (try Earth Balance butter sticks), softened
3-4 tablespoons non-dairy milk
1 1/2 teaspoons vanilla extract