Returning from the brilliant yellow of the canola fields to the original topic...
First, everyone does not know that applesauce is necessarily the BEST replacement for fats, because it isn't always.
Many sorts of fruit and vegetable purees can be used to supplement or replace fats. Prune puree works very, very well in anything chocolate. Squash or pumpkin puree can also work well, as can pureed dried dates, or canned pears, or babyfood carrots, or mangos, or bananas (very good indeed, although they tend to give a banana flavour). Applesauce is blander, true, but it does tend to give the driest results. Choosing fruit based on other flavours of the cake is a better strategy.
Low-fat or nonfat buttermilk or yogourt is excellent as well, particularly in things that are supposed to resemble scones or biscuits as well as in many cake recipes; it produces a nice tenderness. Cottage or Quark cheese can also be used in many instances; it gives good results mixed with a tiny bit of butter - I've used a tablespoon in some recipes, creamed or cut with nonfat dry cottage cheese, and got good stuff.
Other techniques for increasing tenderness and moistness include replacing part of the flour called for with pastry flour if all-purpose. I've also used oat flour (no more than a quarter total) in many cake recipes, which does a lot to counter the dryness.
Dryness, actually, is more often caused by overbaking, or overmixing. Lowfat recipes usually need to be mixed like pancakes - just until combined - and baked to a point that in a regular recipe, might be considered just a smidge underdone.
In cookie recipes, brown rice syrup, oddly enough, is very good. You can find some lowfat cookie recipes using corn syrup and/or molasses; subbing some or all brown rice syrup makes the cookies crisper (anything like a crisp nonfat cookie is often difficult; most recipes are more like little cakes. Which is fine, you know, but sometimes you want something that ISN'T a meringue with a little bit of crunch.)
Pureed silken tofu (the kind in aseptic boxes) can also be used. Like cottage cheese, it tends to work very well in recipes that normally call for creamed butter; one creams a very small amount of butter with tofu blended perfectly smooth.
About sugar: if you're working with published low-fat recipes, they are almost always MUCH MUCH too sweet. Most authors seem to compensate for dropping the fat by increasing the sugar; I find it unnecessary, and usually reduce the sugar by at least 1/3. (I was raised by a European mother, and I'm not much for really sweet things.)
A few references for lowfat baking:
Sandra Woodruff: Secrets of Fat-Free Baking (recipes are much of a muchness, but plenty of tips on using fruit purees and other fat replacers, and converting existing recipes.)
Alice Medrich: Chocolate and the Art of Low Fat Desserts (wonderful)
Patty Neeley: Sweet Deceptions (good if you want something really junky; she uses a lot of nonfat creamer in her recipes, though)
Susan Purdy: Have Your Cake and Eat It Too (she doesn't reduce fat as much as I would, but a good, moderate starting point)
Rose Reisman: Divine Indulgences (again, quite moderate. Some interesting stuff here, including Passover-friendly desserts and a chapter on Soy Sweets.)
Cooking Light has a website at www.cookinglight.com
Sarah Phillips (author of The Healthy Oven Baking Book, which is out of print, but good if you can find it) has a baking website at http://www.cooking911.com/index.htm
which includes a lot of her low-fat baking pointers.
If you want to go all out, check out the searchable archives at www.fatfree.com
This is a huge compilation of recipes from the Fat Free mailing list, including a plethora of desserts. The recipes here are also vegetarian, and often vegan.
There are also a lot of other good low-fat baking resources online. A quick Google search will turn up a pile for you.