Butter substitute for 1 cup of butter for baking What can I substitute for 1 cup of butter in baking recipes (e.g. cookies, muffins, cakes, etc.)?

I'm looking for something that has less saturated fat (and  also doesn't have trans fat).

Update: Since baking is less forgiving than cooking (i.e. if you don't use the exact amount of each ingredient the recipe might fail), could you please also include the amount you would need to use to replace 1 cup of butter?
In muffins and quick breads, I have found that you can actually substitute apple sauce for oil or melted butter. This has worked very well for me!

Use the same amount of apple sauce that you would oil/butter, if not a bit extra.