I tried this today and thought it was a pretty decent hot chocolate substitute:

1 T. unsweetened cocoa powder (like Hersheys)
1 cup water
SF vanilla syrup

Mix the tablespoon of cocoa powder with about a T or two of water in the bottom of a mug until it's a smooth paste. Add a cup of water and microwave until hot. Sweeten with vanilla syrup to taste.

Calories = 20 (for the T. of cocoa powder)