I substitute Splenda for sugar...even the brown sugar in recipes (there's a splenda brown sugar blend) -- just follow the directions on splenda bag about how much to use to sub for real sugar.
I also use the I Can't Believe It's Not Butter SPRAY. It has virtually no calories and no fat. I use that in place of real butter if it calls for little butter. [i use smart balance or Can't Believe It's Not.Butter sticks for using more butter in recipes.]
I replace eggs in recipes with egg whites (you can buy Egg Beaters) in refrigerated section next to reg. eggs at store. This takes cholesterol and fat out...since the yolks of eggs are full of cholesterol! The Egg Beaters box tells you how much EggBeaters to use in place of one egg or 2 eggs, etc.
When a recipe calls for cheese...I use Fat Free Cheese (they have this in shredded and slice form now)....I use Fat Free Mayo....I also have Sugar Free Jelly (peach and strawberry preserves).
Also there's a "healthy choice" or "98% fat free" (or something like that) version of Cream of Mushroom soup. So when a recipe calls for those creamy soup cans...I buy the healthier versions of this.
When using pasta...I always use whole wheat pasta -- they have this in virtually all kinds of pasta now...spaghetti, spirals, wide noodles, penne, lasagna, etc! I even buy the Low-Fat Ragu sauce.
There's a natual peanut butter (that I've only been able to find at Walmart) called Naturally More. It's the best on all its numbers (fat, calories, sat. fat, etc) compared to other natural PB alternatives and it tastes GREAT! Use this to replace PB in recipes. Once you open the jar, you have to refrigerate it but when using it again...I just spoon out the amnt I need into a little bowl, and microwave it for 10 seconds to loosen it up. Works great! And it sooo healthy for you because it contains flaxseed and flaxseed oil!
If I need to grease a pan, or add oil to a hot pan to brown meat or onions...I use Pam non-fat cooking spray -- no oil or butter needed at all! If I need to grease/butter a pan for baking, I use Crisco or Pam spray for baking -- this is fat free too.
When I make chicken fajitas, quesadillas (w/my fat free cheese) or egg burritos (with southwestern EggBeaters and turkey bacon - Oscar Meyer turkey bacon is the best)....i use Carb Balance or the 94% Fat Free tortillas (they have these in white or wheat flour tortillas)...and they taste great. Especially after you warm/toast them a little in a small skillet (no oil/butter) on the stove.