Substitutions

Sugar

Very low-calorie/low-carb substitutes:

Substitute	Ratio	Notes
Stevia extract	Varies by brand; check package	Has a bit of a bitter aftertaste, particularly when used in large quantity.
Erythritol	Use 1&1/3 cups for every cup of sugar	Naturally-occurring sweetener. Has a "cooling" menthol-like effect in large quantity. Needs to be powdered in a spice grinder or Magic Bullet prior to use. Tends to crystallize when cooled, so is not appropriate for creamy items like frosting.
Erythritol + stevia	For 1 cup sugar, use 1 cup erythritol + 1/4 cup equivalent of stevia extract.	Both sweeteners seem to complement one another when used in tandem. Notes for erythritol usage apply.
Xylitol	Replace sugar 1:1	Naturally-occurring sweetener. Needs to be powdered in a spice grinder or Magic Bullet prior to use, but does not crystallize when cooled.
Truvia	Replace sugar 1:1	Commercially-available combination of erythritol and stevia. Notes for erythritol usage apply.
Stevia in the raw	Replace sugar 1:1	Stevia mixed with maltodextrin (a type of corn starch) as a carrier.
Splenda (sucralose)	Replace sugar 1:1	Many people avoid it as it is not a naturally-occurring sweetener.

Natural sweeteners with higher carbs/calories:

Substitute	Ratio	Notes
Unrefined cane sugar	Replace sugar 1:1	Can be called sucanat or turbinado. Contains trace amounts of molasses and has a brown sugar type taste.
Date sugar	Replace sugar 1:1	Ground dehydrated dates.
Coconut sugar	Replace sugar 1:1	Also called palm sugar, coconut crystals, or coconut palm sugar. Similar fructose:glucose ratio as table sugar.
Maple syrup	3/4 cup maple syrup for every cup of sugar	Via foodsubs.com: "Substitute 3/4 cup maple syrup plus 1/4 teaspoon baking soda for each cup of granulated sugar, and reduce another liquid in the recipe by 3 tablespoons."
Honey	3/4 cup honey for every cup of sugar	Via foodsubs.com: "Substitute 3/4 cup honey for each cup of granulated syrup called for in recipe, then reduce another liquid in the recipe by 1/4 cup and add 1/4 teaspoon baking soda (to neutralized the acid in the honey). Reduce oven temperature by 25 degrees--substituting honey for sugar alters the flavor and tends to make baked goods moister, chewier and darker."
Rice syrup	Use 1&3/4 cups rice syrup for every cup of sugar	Rice syrup is comprised of glucose polymers and has almost no fructose! Here is a great post about it on PaleoHacks. Via foodsubs.com: "Substitute 1 3/4 cup rice syrup for each cup of granulated syrup called for in recipe, then reduce another liquid in the recipe by 1/4 cup."
Fruit puree	Varies	Fruit is generally much less sweet so you will have to experiment. Options include applesauce, apple butter, mashed banana, or dried fruit that has been soaked and pureed. You may have to reduce liquid as well.

My thoughts: My top choice is always to reduce or eliminate the amount of added sugar. Super-sweet food tends to promote overconsumption (read more about this in The End of Overeating) so I personally try to keep my palate accustomed to foods that are not supernaturally sweet. I like using whole or minimally-processed fruit as a natural sweetener boost, such as in my recipes for blueberry breakfast sausage, apple butter BBQ drumsticks, or strawberry pulled pork. Sometimes, I add a small amount of honey or molasses because I am after that particular flavor, but not so much to add a ton of sweetness.

I personally categorize dried dates as sugar rather than fruit. By which I mean, I'm not going to create a recipe which uses a cup of mashed dates so that I can slap on a "sugar free" or "Whole 30" label ;) They have a very concentrated candy-like sweetness and pack a ton of sugar while being virtually devoid of nutrition. I'm not saying whether you should or should not eat them, that's your call, I just don't advocate pretending that it's comparable to a handful of fresh blueberries.

Generally speaking, I'm not a huge fan of dried fruit or fruit juice as a sugar substitute. Fruit juice removes the fiber. Dehydration condenses the whole fruit into a sweet little package that can be eaten in a single bite. I may add one or both if I'm seeking that particular flavor or texture, but again, I don't like the idea of using LOTS of fruit in a highly-concentrated form so that I can enjoy the cognitive dissonance of eating "sugar free". That's why you won't find recipes on my site that are sweetened with tons of dried fruit or fruit juice.

If I DO want to make an occasional sweet treat, I prefer a sweetener like stevia or Truvia so that at least I don't have to deal with the blood sugar roller coaster. Ultimately, I will re-iterate that my top choice is just to learn to enjoy food that is less sweet.

P.S. I don't avoid whole, unprocessed fruit in fear of fructose, only the highly-concentrated forms that promote overconsumption. This is a good post explaining the rationale.