Generally considered, the only acceptable sweetener is honey, although some folks are OK with maple syrup. The difference between the two is that honey in its raw state is good to go for making any kind of Paleo dessert, whereas maple syrup needs to be processed (boiled down, in this case) before it actually tastes like anything sweet enough for a cookie.
There are other sugars (stevia, molasses, date sugar etc.) but none of ’em will do your body much good in the forms you can find in a store. The bottom line is that the less sugar you have in your diet, the healthier you’re going to be.
With all that said, remember that how “Paleo” you want to get is up to you. The ultimate Paleo diet has you dropping from a tree onto an elk’s back and slitting his leathery throat with a sharp piece of obsidian… Not many folks are that hardcore. 🙂
Just decide what you’re after with the paleo diet; hard core, great health, tasty food, or any combination and then enjoy the many benefits that eating Primal has to offer.