Another natural product (that DOES have calories, btw, but also does have a low-glycemic rating) is agave syrup.
I found some "light" agave syrup (before my fast) at my health food store, which literally tastes sweet, like liquid sugar. It doesn't even have a taste, like honey does.
I use it when I make lemonade for my child. Real lemons, pure water, and light agave syrup. She's getting a healthy drink she loves...with NO sugar!