Low Calorie Ingredient Substitutions

Oil to Prevent Sticking
Non-stick cooking spray is the low calorie substitute that will keeping food from sticking to the bottom of your pans. Also, use as a substitute for the old grease-and-flour method when baking.
Butter or Oil for Baking
Applesauce or prune puree can replace up to half of the fat (butter, margarine, shortening, or oil) in baked goods such as cakes, brownies, quick breads, muffins, and cookies.
Sunsweet’s Lighter Bake, a product found in the baking aisle at the grocery store, can replace all of the fat and oil in baked goods recipes.

Oil for Marinades and Dressings
Flavored vinegars, such as balsamic, raspberry, and rice vinegar, add exciting flavor to salads and marinades, and are virtually calorie free!
Broths and stocks are also excellent alternatives for marinating meat and chicken.

Sour Cream
Plain, non-fat yogurt works great in casseroles, dips, dressings, as a topping, and anywhere else sour cream is usually used.

Eggs
Two egg whites or 1/4 cup egg substitute (such as Egg Beaters) can replace each whole egg.

Bacon
Turkey bacon, Canadian bacon, or lean smoked ham provides a lower-calorie substitute, retaining the smoky flavor that bacon is known for.

Light Cream
Combine equal parts 1% milk and evaporated skim milk, and use in cream soups and sauces.

Whole Milk
Reduced fat milk (2%, 1% or skim) makes a lower calorie alternative to full-fat whole milk.

Whipped Cream
Evaporated skim milk can be whipped with a little sugar and vanilla extract into a fluffy dessert topping (note: the milk and the beaters must be very cold, but not frozen, before whipping).

Sugar
Splenda is a sugar replacement product that performs well in sweets and baked goods, and is calorie-free. Use Splenda No Calorie Sweetener Granular for items like pie filling, cheesecake, and sweet sauce. Opt for the Splenda Sugar Blend for Baking in baked good such as cakes, brownies, and muffins. Although the Sugar Blend for Baking is half real sugar (therefore higher in calories), it provides a much more desirable outcome for baked goods than using the granular product. (Note: There has been some controversy over the safety of sweeteners such as Splenda. Depending on your personal preference toward sweeteners, you may or may not choose to use Splenda. About.com's Guide to Nutrition offers more information, about this sweetener.)

From About.com - http://lowcaloriecooking.about.com/od/lowcaloriebasics/tp/LowCalorieSubstitutions.htm