I am big into baking and most of recipes are lower in sugar/fat/cholesterol than regular cookies because of simply subs. I rarely, if ever, use eggs and I try to use the least amount of sugar possible.
http://dancingveggies.blogspot.com for recipes (all cookies on site are under 60calories per based on the nutrition calculator used by The Tasty Kitchen)
Butter can be tricky, but always go for ones like Earth Balance or Smart Balance which are unsalted and low in trans-fat. Soy butters can also be used but make sure to check the label because many of them are just as bad as regular.
Instead of using eggs I use applesauce (1/3 cup to 1 large egg) or a banana (1/2 to 1 medium egg plus 1tbsp water) depending on the recipe. I have also heard of people using cream of tarter but I'm not sure of that ratio. Instead of using all-purpose flour I try to go half organic whole wheat or switch out for a half cup of oats (in both cases just a 1:1 ratio). Instead of using vanilla extract I try to use pure maple syrup (just half what is called for), a no-sugar added 100% fruit juice, or leave it out. When it comes to white sugar I add it slowly, and taste the dough to see if it really needs it. I also switch in some raw brown sugar which has a stronger taste than white sugar, so you wind up using less of it.
Final trick: half the recipe and/or half the size of the cookies/cake slices. Not only are there half of the sinful treasures around but halving the size of the cookie will trick your brain much like using a smaller plate will. So you tell yourself you can have two cookies but in reality you are only eating the calories found in one cookie. Also make sure to use a small dessert plate for baked goods, you'll eat them slower that way and give your stomach more time to send those triggers saying you are stuffed!

It's not just butter that has a bad rap. Don't forget, baked goods are made with sugar (empty calories) and flour (carbohydrate-heavy).

There are some good butter substitutes, instead of oil, you could look into. Check the butter aisle at the store. One brand we like for spreading on toast and such is called Smart Balance and I think they have a version you can bake with.

In the end, I believe you should always bake with the best ingredients, and eat the final product in moderation. And share the wealth!!!!!! My Neighbors, friends, coworkers, teachers, my pals at the library, at church, all love me (and/or hate me, depending on how you look at it) very much. ;-)

Instead of thinking about substitutes, maybe seek out recipes that are inherently lowfat/butter-free etc. like angel food cake, fruit crisp, macarons, cakes leavened with buttermilk. I have come across pie crust recipes that use one egg and about half the butter of other recipes but the texture is not flaky like a butter or shortening crust. Good luck!

Butter yields the best results. I don't make substitutions, generally. I will bake some vegan goods- particularly quick breads- with oil, applesauce or pumpkin puree. I am generally more concerned about the quantity of sugar than butter, and I try to make less sweet baked goods more than anything else. I try to limit indulgent baked goods to special occasions and/or the occasional bad day. I always give the majority to my husband to take to his office- full of scientists and engineers (mostly men) who are less concerned about counting calories.

I would check out Heidi Swanson's site, 101cookbooks.com She advocates using the best ingredients possible, and using a variety of different oils in her cooking. I've baked several of her cookie recipes with good results. Also, you can compensate in other ways. Throw in some whole wheat flour or spelt flour into a forgiving recipe- if you can't cut back the butter, at least you can add some extra fiber or protein.

I agree to seek out recipes from trusted sources. Cooking Light does reasonably good lower fat baked goods.I used to especially like a banana bread I have lost the recipe to. Here is a little primer from them:
http://www.cookinglight.com/cooking-101/techniques/the-art-of-low-fat-baking-00400000001071/

Alice Medrich has a lower calorie desserts book Chocolate and the Art of Low-Fat desserts that would be worth seeking out, it won a James Beard award,

Cut calories/fat somewhere else, bake less often, eat tiny pieces. Betteirene told the Truth about the substitutes, so remember, if it's really really good, you don't need to eat as much to feel satisfied. Enjoy other people's enjoyment. Bake 2 cookies at a time. The rest of the dough will keep till tomorrow.

Hershey's website does have a great chocolate cake made with oil (and you can use better cocoa.)

Baking Rule #1, also known as The Golden Rule: There is no substitute for butter--nothing else on earth can duplicate the taste and texture it gives to baked goods. If a recipe calls for it, use real butter. Period.

That said, when I was a health-food hippie in the 60s, I tried all kinds of substitutes for butter and eggs. Some of them worked, some didn't, and none of them got written down in my cookbook because none of them were keepers. I wasted all kinds of time and money before deciding that my efforts were worthless. You'd do much better if you let someone else do the experimenting and the measuring (and the wasting). Unless you have all kinds of time and money, practice with their recipes first, getting a feel for the substitutions, before doing it yourself.

You can search for vegan/vegetarian recipes, diabetic recipes, heart-healthy recipes, but I think the best place to start would be a web site devoted to mothers of picky eaters; such moms are awfully inventive at finding ways of smuggling/disguising/disfiguring butternut squash into chocolate chip cookies.

And if you invent something heavenly, please don't forget to post it somewhere on food52. I, for one, would welcome it with open arms. And mouth.

Take up bread baking - especially whole grain bread baking. All the baking without the butter. (Or give away your baked goods after your family has had a little bit.)

Baking is my first love, so I feel your pain, too. I like the suggestions drbabs offered.

Before I moved, I had a small, successful baking/catering business on the side. I was constantly testing new recipes/variations, and I often brought the goodies to work for my coworkers. They particularly enjoyed it when I brought different variations of the same recipe, left a piece of paper in the breakroom, and asked them to comment on their favorite/least favorite and why. It added a little excitement to the day for them, and I wasn't stuck with four variations of yellow cake at home - win win. :)

I've used beans in baked goods and have mixed feelings about it. They DO cut the fat and give moisture, but there are pretty significant textural/flavor differences. If you're craving a brownie and you're used to full-fat brownies, chances are you won't be satisfied with a black bean brownie because it's not the brownie your brain/tastebuds know to crave.. ya know? (Not knocking bean-baking.. it definitely has its place.)

Overall, I agree with Mr Vittles.. If you're craving a baked good, best to make the full-fat version, keep a portion of it, and send the rest out into the world. Or you could try tweaking your recipes to create smaller batches, though some recipes are finicky about that kind of thing. Good luck!

Hmm... If you don't want to worry about growing out of your clothes try eating less of your baked goods, instead of substituting butter. You can find substitutions, but they will all yield inferior results. If you cannot stand seeing your baked goods sit at home, try giving them out to coworkers or family. That way you'll at least gain some new friends instead of few extra lb's.

I love to bake, too, so I feel your pain. The answer is, it depends. Full fat definitely tastes best, and I'm a big believer that a small taste of something wonderful beats a lot of something mediocre. So I tend to use all butter and eat only one cooke or a sliver of pie or cake if I'm watching my weight. (My co-workers love me. :)) But you can do some low fat substituting. In most cakelike recipes you can replace about 1/2 of the fat with an equal amount of unsweetened applesauce or pureed prunes to little ill effect--the cake will be moister and stickier and not ideal, but still tasty. I have not substituted beans, but I know there are vegan chefs who do. I wouldn't substitute more than half, though. In high school for her science project, my dayghter made 3 batches of brownies using a favorite recipe, and substituted 1/2 applesauce in one and all applesauce in the other. The full fat was best, the 1/2 applesauce was OK, the all-applesauce was sticky and not very good. I hope this helps!