Here are a couple that I like to use:
1. Oatmeal, water, butter and peanut butter
2. Oatmeal, 1/2 amount of milk, 1/2 amount of cream, butter, a cinnamon stick and a little brown or white sugar
3. Plain & Simple: Oatmeal, water, butter and brown sugar
Some other things to add that are always good are Raisins or Craisins.