Now that I make my own yogurt with my hand dandy Salton yogurt maker, I have begun to substitute yogurt for oil and butter in baking recipes.
See Yogurt for Lower-Fat Baking at Taste of Home. These do not wholly substitute yogurt for oil or butter.
Here are recipes for Cranberry Yogurt Muffins , Lemon Honey Muffins, and Whole Grain Banana Muffins with no oil or butter. Yogurt(and apple sauce in some of these) completely replaces the oils. More: Whole Wheat Maple Quick Bread, Ginger Biscuits , and Walnut Wheat Bread
You can find butter extract flavoring in the spice aisle at the grocery to give baking without butter more flavor. I have not tried this but may if I can find it.