My son is diabetic and I often used this website:
http://www.easy-diabetic-recipes.com/
And the link to brownie recipes:
http://www.easy-diabetic-recipes.com/diabetic-brownie-recipes.html
My Dad was diabetic and I used to find great recipes on-line.
Here are a few:
http://allrecipes.com//Recipe/sugar-free-brownies/Detail.aspx
http://www.naturesnaturalhealing.com/recipes/diabetic/desserts.shtml#Brownies
http://www.cooksrecipes.com/diabetic/double_chocolate_brownies_recipe.html