Splenda, Sweet One, Swiss Sweet, or Sunettmakes great substitutes for sugar in cake recipes. You can get it a most supermarkets and it's used cup for cup.

Use your favorite cake recipe except substitute Splenda Granular. According to the Splenda instructions to achieve a better rise you should also add 1/2 cup nonfat dry milk powder and 1/2 teaspoon of baking powder for every cup of Splenda used. You will also need to check the cake 7-10 minutes earlier than your recipe calls for as your cake will bake more quickly than a cake that is made with sugar.